From: David Hildenbrand <hidden> Date: 2021-04-08 09:20:37
Trying to set CONFIG_CMA=y with CONFIG_DMA_CMA=n revealed that we have
three drivers that select these options. Random drivers should not
override user settings of such core knobs. Let's use "imply DMA_CMA"
instead, such that user configuration and dependencies are respected.
Cc: Joel Stanley <joel@jms.id.au>
Cc: David Airlie <redacted>
Cc: Daniel Vetter <redacted>
Cc: Andrew Jeffery <redacted>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Russell King <linux+etnaviv@armlinux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Bartlomiej Zolnierkiewicz <redacted>
Cc: Linus Walleij <redacted>
Cc: Michal Simek <redacted>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Randy Dunlap <redacted>
Cc: Peter Collingbourne <redacted>
Cc: linux-aspeed@lists.ozlabs.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: etnaviv@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
David Hildenbrand (2):
drivers/video/fbdev: don't select DMA_CMA
drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv
drivers/gpu/drm/aspeed/Kconfig | 3 +--
drivers/gpu/drm/etnaviv/Kconfig | 3 +--
drivers/video/fbdev/Kconfig | 2 +-
3 files changed, 3 insertions(+), 5 deletions(-)
--
2.30.2
From: David Hildenbrand <hidden> Date: 2021-04-08 09:20:44
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS or CMA right now.
Signed-off-by: David Hildenbrand <redacted>
---
drivers/video/fbdev/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
From: David Hildenbrand <hidden> Date: 2021-04-08 09:20:49
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
Signed-off-by: David Hildenbrand <redacted>
---
drivers/gpu/drm/aspeed/Kconfig | 3 +--
drivers/gpu/drm/etnaviv/Kconfig | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
From: Mike Rapoport <rppt@kernel.org> Date: 2021-04-08 09:56:17
On Thu, Apr 08, 2021 at 11:20:10AM +0200, David Hildenbrand wrote:
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
^ DMA_CMA ?
quoted hunk
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS or CMA right now.
Signed-off-by: David Hildenbrand <redacted>
---
drivers/video/fbdev/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
From: Mike Rapoport <rppt@kernel.org> Date: 2021-04-08 09:57:08
On Thu, Apr 08, 2021 at 11:20:11AM +0200, David Hildenbrand wrote:
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
^ DMA_CMA
quoted hunk
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
Signed-off-by: David Hildenbrand <redacted>
---
drivers/gpu/drm/aspeed/Kconfig | 3 +--
drivers/gpu/drm/etnaviv/Kconfig | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
From: David Hildenbrand <hidden> Date: 2021-04-08 09:57:45
On 08.04.21 11:56, Mike Rapoport wrote:
On Thu, Apr 08, 2021 at 11:20:11AM +0200, David Hildenbrand wrote:
quoted
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
^ DMA_CMA
quoted
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
Signed-off-by: David Hildenbrand <redacted>
---
drivers/gpu/drm/aspeed/Kconfig | 3 +--
drivers/gpu/drm/etnaviv/Kconfig | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand [off-list ref] wrote:
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more
problems than it solves.
In particular, it does not prevent a configuration with 'DRM_CMA=m'
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
If you want this kind of soft dependency, you need
'depends on DRM_CMA || !DRM_CMA'.
Arnd
From: David Hildenbrand <hidden> Date: 2021-04-08 10:27:22
On 08.04.21 12:20, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand [off-list ref] wrote:
quoted
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more
problems than it solves.
I thought that was the case with "select" :)
In particular, it does not prevent a configuration with 'DRM_CMA=m'
I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work
just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
If you want this kind of soft dependency, you need
'depends on DRM_CMA || !DRM_CMA'.
Seriously? I think the point of imply is "please enable if possible and
not prevented by someone else". Your example looks more like a NOP - no?
Or will it have the same effect?
--
Thanks,
David / dhildenb
From: David Hildenbrand <hidden> Date: 2021-04-08 10:37:54
On 08.04.21 12:27, David Hildenbrand wrote:
On 08.04.21 12:20, Arnd Bergmann wrote:
quoted
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand [off-list ref] wrote:
quoted
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more
problems than it solves.
I thought that was the case with "select" :)
quoted
In particular, it does not prevent a configuration with 'DRM_CMA=m'
I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
quoted
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work
just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
quoted
If you want this kind of soft dependency, you need
'depends on DRM_CMA || !DRM_CMA'.
Seriously? I think the point of imply is "please enable if possible and
not prevented by someone else". Your example looks more like a NOP - no?
Or will it have the same effect?
I just tried (remove CONFIG_DMA_CMA from .config followed by make) and
the default will be set to "N" (when querying the user). So it indeed
looks like a NOP - unless I am missing something.
--
Thanks,
David / dhildenb
On Thu, Apr 8, 2021 at 12:29 PM David Hildenbrand [off-list ref] wrote:
On 08.04.21 12:20, Arnd Bergmann wrote:
quoted
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand [off-list ref] wrote:
quoted
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more
problems than it solves.
I thought that was the case with "select" :)
Yes, but that's a different set of problems
quoted
In particular, it does not prevent a configuration with 'DRM_CMA=m'
I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
Ok, at least that makes it easier.
quoted
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work
just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
I thought you were trying to solve the problem where DRMA_ASPEED_GFX
can optionally link against CMA but would fail to build when the CMA code
is in a loadable module.
If the problem you are trying to solve is a different one, you need a different
solution, not what I posted above.
quoted
If you want this kind of soft dependency, you need
'depends on DRM_CMA || !DRM_CMA'.
Seriously? I think the point of imply is "please enable if possible and
not prevented by someone else".
That used to be the meaning, but it changed a few years ago. Now
it means "when a used manually turns on this symbol, turn on the
implied one as well, but let them turn it off again if they choose".
This is pretty much a NOP.
Your example looks more like a NOP - no?
Or will it have the same effect?
The example I gave is only meaningful if both are tristate, which is
not the case here as you explain.
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
Arnd
From: David Hildenbrand <hidden> Date: 2021-04-08 11:01:03
quoted
quoted
In particular, it does not prevent a configuration with 'DRM_CMA=m'
I assume you meant "DRM_CMA=n" ? DRM_CMA cannot be built as a module.
Ok, at least that makes it easier.
quoted
quoted
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
I don't follow. "DRM_CMA=n" and 'DRMA_ASPEED_GFX=y' is supposed to work
just fine (e.g., without HAVE_DMA_CONTIGUOUS) or what am I missing?
I thought you were trying to solve the problem where DRMA_ASPEED_GFX
can optionally link against CMA but would fail to build when the CMA code
is in a loadable module.
Yes. I was trying to say: it works with this patch just fine. The issue
you described does not seem to apply (DRM_CMA=m).
quoted
Your example looks more like a NOP - no?
Or will it have the same effect?
The example I gave is only meaningful if both are tristate, which is
not the case here as you explain.
Okay, thanks.
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
What would be the right thing to do in the case here then to achieve the
"if DRMA_ASPEED_GFX is enabled, also enable DMA_CMA id possible"?
One approach could be to have for DMA_CMA
default y if DRMA_ASPEED_GFX
but it feels like the wrong way to tackle this.
Thanks!
--
Thanks,
David / dhildenb
From: Daniel Vetter <hidden> Date: 2021-04-08 11:38:25
On Thu, Apr 08, 2021 at 12:20:50PM +0200, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 11:22 AM David Hildenbrand [off-list ref] wrote:
quoted
Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n). Use "imply" instead, to still respect
dependencies and manual overrides.
"This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt."
Implying DRM_CMA should be sufficient, as that depends on CMA.
Note: If this is a real dependency, we should use "depends on DMA_CMA"
instead - but I assume the driver can work without CMA just fine --
esp. when we wouldn't have HAVE_DMA_CONTIGUOUS right now.
'imply' is almost never the right solution, and it tends to cause more
problems than it solves.
In particular, it does not prevent a configuration with 'DRM_CMA=m'
and 'DRMA_ASPEED_GFX=y', or any build failures from such
a configuration.
If you want this kind of soft dependency, you need
'depends on DRM_CMA || !DRM_CMA'.
The problem is that depends on is a real pain for users to find their
drivers. This is why we have a ton of select, because the kconfig ui tends
to suck.
If you want to change this, we need automatic conflict resolution like apt
and other package managers have, with suggestions how to fix the config if
you want to enable a driver, but some of its requirements are missing. The
current approach of hiding driver symbols complete if any of their
dependencies are off is really not great.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand [off-list ref] wrote:
quoted
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
What would be the right thing to do in the case here then to achieve the
"if DRMA_ASPEED_GFX is enabled, also enable DMA_CMA id possible"?
One approach could be to have for DMA_CMA
default y if DRMA_ASPEED_GFX
but it feels like the wrong way to tackle this.
I'm still not sure what you are trying to achieve. Is the idea only to provide
a useful default for DMA_CMA depending on which drivers are enabled?
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
From: David Hildenbrand <hidden> Date: 2021-04-08 12:01:29
On 08.04.21 13:44, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
What would be the right thing to do in the case here then to achieve the
"if DRMA_ASPEED_GFX is enabled, also enable DMA_CMA id possible"?
One approach could be to have for DMA_CMA
default y if DRMA_ASPEED_GFX
but it feels like the wrong way to tackle this.
I'm still not sure what you are trying to achieve. Is the idea only to provide
a useful default for DMA_CMA depending on which drivers are enabled?
"Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n)."
Let's assume I'm a distribution and want to set CONFIG_CMA=n or want to
set CONFIG_DMA_CMA=n with CONFIG_CMA=y; there is no way to do that with
e.g., DRMA_ASPEED_GFX=y because it will always override my (user!)
setting -- even though it doesn't really always need it. Using "select"
is the problem here.
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
I wondered if there is a better approach to achieve the same; "imply"
sounded like a good candidate.
--
Thanks,
David / dhildenb
On Thu, Apr 8, 2021 at 2:00 PM David Hildenbrand [off-list ref] wrote:
On 08.04.21 13:44, Arnd Bergmann wrote:
quoted
On Thu, Apr 8, 2021 at 1:00 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
It is a somewhat awkward way to say "prevent this symbol from
being =y if the dependency is =m".
What would be the right thing to do in the case here then to achieve the
"if DRMA_ASPEED_GFX is enabled, also enable DMA_CMA id possible"?
One approach could be to have for DMA_CMA
default y if DRMA_ASPEED_GFX
but it feels like the wrong way to tackle this.
I'm still not sure what you are trying to achieve. Is the idea only to provide
a useful default for DMA_CMA depending on which drivers are enabled?
"Random drivers should not override a user configuration of core knobs
(e.g., CONFIG_DMA_CMA=n)."
Let's assume I'm a distribution and want to set CONFIG_CMA=n or want to
set CONFIG_DMA_CMA=n with CONFIG_CMA=y; there is no way to do that with
e.g., DRMA_ASPEED_GFX=y because it will always override my (user!)
setting -- even though it doesn't really always need it. Using "select"
is the problem here.
I agree on the part of removing the 'select' if we don't need it. The
part I couldn't figure out was what the 'imply' is supposed to help with.
Most other users that added imply tried (and failed) to fix a build problem.
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
I wondered if there is a better approach to achieve the same; "imply"
sounded like a good candidate.
I can probably find a couple more, but regardless of how many others
exist, this would be a much clearer way of doing it than 'imply' since it
has none of the ambiguity and misuse problems.
I think the reason we don't see more is that generally speaking, those
defaults are widely ignored anyway. You almost always start out with
a defconfig file that contains everything you know you need, and then
you add bits to that. Having the default in any form only helps to
make that defconfig file one line shorter, while requiring other users
to add another line to turn it off when they do not want it.
Arnd
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
drivers/gpu/drm/mcde/Kconfig
drivers/gpu/drm/pl111/Kconfig
drivers/gpu/drm/tve200/Kconfig
certainly needs this as well, and pretty much anything that is
selecting DRM_KMS_CMA_HELPER or
DRM_GEM_CMA_HELPER "wants" DMA_CMA.
Yours,
Linus Walleij
On Thu, Apr 8, 2021 at 2:50 PM Linus Walleij [off-list ref] wrote:
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
drivers/gpu/drm/mcde/Kconfig
drivers/gpu/drm/pl111/Kconfig
drivers/gpu/drm/tve200/Kconfig
certainly needs this as well, and pretty much anything that is
selecting DRM_KMS_CMA_HELPER or
DRM_GEM_CMA_HELPER "wants" DMA_CMA.
Are there any that don't select either of the helpers and
still want CMA? If not, it would be easy to just add
default DRM_KMS_CMA_HELPER || DRM_GEM_CMA_HELPER
and skipt the extra symbol.
Arnd
From: David Hildenbrand <hidden> Date: 2021-04-08 16:44:41
On 08.04.21 14:49, Linus Walleij wrote:
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
:) I actually wanted to convert them to "depends on DMA_CMA" but ran
into recursive dependencies ...
From: Jason Gunthorpe <jgg@ziepe.ca> Date: 2021-04-08 16:46:17
On Thu, Apr 08, 2021 at 01:38:17PM +0200, Daniel Vetter wrote:
If you want to change this, we need automatic conflict resolution like apt
and other package managers have, with suggestions how to fix the config if
you want to enable a driver, but some of its requirements are missing. The
current approach of hiding driver symbols complete if any of their
dependencies are off is really not great.
+1 to this..
Though Kconfig is basically already unusuable unless you have hours to
carefully craft the kconfig you need to get out.
I'm not sure trying to optimize this by abusing the existing language
rules is such a good idea.
I gave a very half hearted go at a simple heuristic solution solve for
kconfig a while ago. It is good enough to sometimes automate a kconfig
task, but it is not so nice.
I use it to do things like "turn on all RDMA drivers" which is quite
a hard to do by hand.
It looks liked heursitics need a lot of fine tuning as the
conditionals are complex enough that it is hard to guess which branch
is going to yield a success.
Jason
On Thu, Apr 8, 2021 at 6:45 PM David Hildenbrand [off-list ref] wrote:
On 08.04.21 14:49, Linus Walleij wrote:
quoted
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
:) I actually wanted to convert them to "depends on DMA_CMA" but ran
into recursive dependencies ...
Right, this is the main problem caused by using 'select' to
force-enable symbols that other drivers depend on.
Usually, the answer is to be consistent about the use of 'select'
and 'depends on', using the former only to enable symbols that
are hidden, while using 'depends on' for anything that is an
actual build time dependency.
I was assuming these are "real" dependencies. Will it also work without
DMA_CMA?
I think in this case, it is fairly likely to work without DMA_CMA when the
probe function gets called during a fresh boot, but fairly likely to fail if
it gets called after the system has run for long enough to fragment the
free memory.
The point of DMA_CMA is to make it work reliably.
Arnd
I was assuming these are "real" dependencies. Will it also work without
DMA_CMA?
It will mostly work but that is only because the reservations are
mostly contiguous anyway because they are done early and
are small. The hardware requires contiguous buffers in all
three cases. I'm not sure I always got it right.
quoted
certainly needs this as well, and pretty much anything that is
selecting DRM_KMS_CMA_HELPER or
DRM_GEM_CMA_HELPER "wants" DMA_CMA.
"wants" as in "desires to use but can life without" or "wants" as in
"really needs it". ?
I don't know the exact semantics of using DRM_KMS_CMA*
without actually using DMA_CMA. I suspect small allocations
will be contiguous and big allocations will start to fragment?
but it's just my guess. I guess "really need it"?
Yours,
Linus Walleij
From: David Hildenbrand <hidden> Date: 2021-04-09 08:07:19
On 08.04.21 15:19, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 2:50 PM Linus Walleij [off-list ref] wrote:
quoted
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
drivers/gpu/drm/mcde/Kconfig
drivers/gpu/drm/pl111/Kconfig
drivers/gpu/drm/tve200/Kconfig
certainly needs this as well, and pretty much anything that is
selecting DRM_KMS_CMA_HELPER or
DRM_GEM_CMA_HELPER "wants" DMA_CMA.
Are there any that don't select either of the helpers and
still want CMA? If not, it would be easy to just add
default DRM_KMS_CMA_HELPER || DRM_GEM_CMA_HELPER
and skipt the extra symbol.
That sounds like a reasonable thing to do. I'll look into that.
--
Thanks,
David / dhildenb
From: David Hildenbrand <hidden> Date: 2021-04-09 08:10:07
On 08.04.21 22:29, Arnd Bergmann wrote:
On Thu, Apr 8, 2021 at 6:45 PM David Hildenbrand [off-list ref] wrote:
quoted
On 08.04.21 14:49, Linus Walleij wrote:
quoted
On Thu, Apr 8, 2021 at 2:01 PM David Hildenbrand [off-list ref] wrote:
quoted
quoted
This is something you could do using a hidden helper symbol like
config DRMA_ASPEED_GFX
bool "Aspeed display driver"
select DRM_WANT_CMA
config DRM_WANT_CMA
bool
help
Select this from any driver that benefits from CMA being enabled
config DMA_CMA
bool "Use CMA helpers for DRM"
default DRM_WANT_CMA
Arnd
That's precisely what I had first, with an additional "WANT_CMA" -- but
looking at the number of such existing options (I was able to spot 1 !)
If you do this it probably makes sense to fix a few other drivers
Kconfig in the process. It's not just a problem with your driver.
"my" drivers:
:) I actually wanted to convert them to "depends on DMA_CMA" but ran
into recursive dependencies ...
Right, this is the main problem caused by using 'select' to
force-enable symbols that other drivers depend on.
Usually, the answer is to be consistent about the use of 'select'
and 'depends on', using the former only to enable symbols that
are hidden, while using 'depends on' for anything that is an
actual build time dependency.
quoted
I was assuming these are "real" dependencies. Will it also work without
DMA_CMA?
I think in this case, it is fairly likely to work without DMA_CMA when the
probe function gets called during a fresh boot, but fairly likely to fail if
it gets called after the system has run for long enough to fragment the
free memory.
The point of DMA_CMA is to make it work reliably.
Right, and even at runtime there is no guarantee that DMA_CMA will do
anything -- especially if we don't reserve a CMA region (e.g., "cma=X").
So this really sounds like a
"desires DMA_CMA"
and achieving that via an additional symbol or via "default y if ..."
for DMA_CMA sounds reasonable.
Thanks!
--
Thanks,
David / dhildenb