Re: [PATCH 3/3] PCI: Convert rtw88 power cycle quirk to shutdown quirk

Kai-Heng Feng [off-list ref] writes:

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

-- 
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

On 26.02.2021 08:12, Kalle Valo wrote:

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

On Fri, Feb 26, 2021 at 8:10 PM Heiner Kallweit [off-list ref] wrote:

On 26.02.2021 08:12, Kalle Valo wrote:

quoted

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

To make putting device to D3 more generic, as there are more than one
device need the quirk.

Here's the discussion:
https://lore.kernel.org/linux-usb/00de6927-3fa6-a9a3-2d65-2b4d4e8f0012@linux.intel.com/

Kai-Heng

On 26.02.2021 13:18, Kai-Heng Feng wrote:

On Fri, Feb 26, 2021 at 8:10 PM Heiner Kallweit [off-list ref] wrote:

quoted

On 26.02.2021 08:12, Kalle Valo wrote:

quoted

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

To make putting device to D3 more generic, as there are more than one
device need the quirk.

Here's the discussion:
https://lore.kernel.org/linux-usb/00de6927-3fa6-a9a3-2d65-2b4d4e8f0012@linux.intel.com/

Thanks for the link. For the AMD USB use case I don't have a strong opinion,
what's considered the better option may be a question of personal taste.
For rtw88 however I'd still consider it over-engineering to replace a simple
call to pci_set_power_state() with a PCI quirk.
I may be biased here because I find it sometimes bothering if I want to
look up how a device is handled and in addition to checking the respective
driver I also have to grep through quirks.c whether there's any special
handling.

Kai-Heng

Heiner

On Fri, Feb 26, 2021 at 02:31:31PM +0100, Heiner Kallweit wrote:

On 26.02.2021 13:18, Kai-Heng Feng wrote:

quoted

On Fri, Feb 26, 2021 at 8:10 PM Heiner Kallweit [off-list ref] wrote:

quoted

On 26.02.2021 08:12, Kalle Valo wrote:

quoted

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

To make putting device to D3 more generic, as there are more than one
device need the quirk.

Here's the discussion:
https://lore.kernel.org/linux-usb/00de6927-3fa6-a9a3-2d65-2b4d4e8f0012@linux.intel.com/

Thanks for the link. For the AMD USB use case I don't have a strong opinion,
what's considered the better option may be a question of personal taste.
For rtw88 however I'd still consider it over-engineering to replace a simple
call to pci_set_power_state() with a PCI quirk.
I may be biased here because I find it sometimes bothering if I want to
look up how a device is handled and in addition to checking the respective
driver I also have to grep through quirks.c whether there's any special
handling.

I haven't looked at these patches carefully, but in general, I agree
that quirks should be used to work around hardware defects in the
device.  If the device behaves correctly per spec, we should use a
different mechanism so the code remains generic and all devices get
the benefit.

If we do add quirks, the commit log should explain what the device
defect is.

Bjorn

On Sat, Feb 27, 2021 at 2:17 AM Bjorn Helgaas [off-list ref] wrote:

On Fri, Feb 26, 2021 at 02:31:31PM +0100, Heiner Kallweit wrote:

quoted

On 26.02.2021 13:18, Kai-Heng Feng wrote:

quoted

On Fri, Feb 26, 2021 at 8:10 PM Heiner Kallweit [off-list ref] wrote:

quoted

On 26.02.2021 08:12, Kalle Valo wrote:

quoted

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

To make putting device to D3 more generic, as there are more than one
device need the quirk.

Here's the discussion:
https://lore.kernel.org/linux-usb/00de6927-3fa6-a9a3-2d65-2b4d4e8f0012@linux.intel.com/

Thanks for the link. For the AMD USB use case I don't have a strong opinion,
what's considered the better option may be a question of personal taste.
For rtw88 however I'd still consider it over-engineering to replace a simple
call to pci_set_power_state() with a PCI quirk.
I may be biased here because I find it sometimes bothering if I want to
look up how a device is handled and in addition to checking the respective
driver I also have to grep through quirks.c whether there's any special
handling.

I haven't looked at these patches carefully, but in general, I agree
that quirks should be used to work around hardware defects in the
device.  If the device behaves correctly per spec, we should use a
different mechanism so the code remains generic and all devices get
the benefit.

If we do add quirks, the commit log should explain what the device
defect is.

So maybe it's reasonable to put all PCI devices to D3 at shutdown?

Kai-Heng

Bjorn

[+cc Rafael, linux-pm]

On Thu, Mar 04, 2021 at 02:07:18PM +0800, Kai-Heng Feng wrote:

On Sat, Feb 27, 2021 at 2:17 AM Bjorn Helgaas [off-list ref] wrote:

quoted

On Fri, Feb 26, 2021 at 02:31:31PM +0100, Heiner Kallweit wrote:

quoted

On 26.02.2021 13:18, Kai-Heng Feng wrote:

quoted

On Fri, Feb 26, 2021 at 8:10 PM Heiner Kallweit [off-list ref] wrote:

quoted

On 26.02.2021 08:12, Kalle Valo wrote:

quoted

Kai-Heng Feng [off-list ref] writes:

quoted

Now we have a generic D3 shutdown quirk, so convert the original
approach to a PCI quirk.

Signed-off-by: Kai-Heng Feng <redacted>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 2 --
 drivers/pci/quirks.c                     | 6 ++++++
 2 files changed, 6 insertions(+), 2 deletions(-)

It would have been nice to CC linux-wireless also on patches 1-2. I only
saw patch 3 and had to search the rest of patches from lkml.

I assume this goes via the PCI tree so:

Acked-by: Kalle Valo <redacted>

To me it looks odd to (mis-)use the quirk mechanism to set a device
to D3cold on shutdown. As I see it the quirk mechanism is used to work
around certain device misbehavior. And setting a device to a D3
state on shutdown is a normal activity, and the shutdown() callback
seems to be a good place for it.
I miss an explanation what the actual benefit of the change is.

To make putting device to D3 more generic, as there are more than one
device need the quirk.

Here's the discussion:
https://lore.kernel.org/linux-usb/00de6927-3fa6-a9a3-2d65-2b4d4e8f0012@linux.intel.com/

Thanks for the link. For the AMD USB use case I don't have a strong opinion,
what's considered the better option may be a question of personal taste.
For rtw88 however I'd still consider it over-engineering to replace a simple
call to pci_set_power_state() with a PCI quirk.
I may be biased here because I find it sometimes bothering if I want to
look up how a device is handled and in addition to checking the respective
driver I also have to grep through quirks.c whether there's any special
handling.

I haven't looked at these patches carefully, but in general, I agree
that quirks should be used to work around hardware defects in the
device.  If the device behaves correctly per spec, we should use a
different mechanism so the code remains generic and all devices get
the benefit.

If we do add quirks, the commit log should explain what the device
defect is.

So maybe it's reasonable to put all PCI devices to D3 at shutdown?

I don't know off-hand.  I added Rafael and linux-pm in case they do.

If not, I suggest working up a patch to do that and a commit log that
explains why that's a good idea and then we can have a discussion
about it.  This thread really doesn't have that justification.  It
says "putting device X in D3cold at shutdown saves 0.03w while in S5",
but doesn't explain why that's safe or desirable for all devices.

Bjorn