On 22 October 2015 at 23:27, Scott Wood [off-list ref] wrote:

On Thu, 2015-10-22 at 15:04 +0200, Tomeu Vizoso wrote:

quoted

On 22 October 2015 at 00:51, Scott Wood [off-list ref] wrote:

quoted

On Wed, 2015-10-21 at 08:44 -0500, Rob Herring wrote:

quoted

On Wed, Oct 21, 2015 at 12:54 AM, Scott Wood [off-list ref]
wrote:

quoted

On Mon, 2015-09-21 at 16:03 +0200, Tomeu Vizoso wrote:

quoted

Instead of trying to match and probe platform and AMBA devices right
after each is registered, delay their probes until
device_initcall_sync.

This means that devices will start probing once all built-in drivers
have registered, and after all platform and AMBA devices from the DT
have been registered already.

This allows us to prevent deferred probes by probing dependencies on
demand.

Signed-off-by: Tomeu Vizoso <redacted>
---

Changes in v4:
- Also defer probes of AMBA devices registered from the DT as they
can
  also request resources.

 drivers/of/platform.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

This breaks arch/powerpc/sysdev/fsl_pci.c.  The PCI bus is an OF
platform
device, and it must be probed before pcibios_init() which is a
subsys_initcall(), or else the PCI bus never gets scanned.

Thanks for the report. This is probably getting dropped, but it could
be disabled for PPC.

I don't think that adding another arbitrary arch difference would be the
right solution.

I think Rob meant temporarily disable it while things get fixed. At
least,

So, what is the permanent fix for the swiotlb issue (or more generally, the
inability to have a late_initcall that runs after non-module, non-hotplug
platform devices have been probed)?

If the code in pcibios_init() depends on the PCI bus device having
probed, then I would recommend making that dependency explicit by
calling of_device_probe() on the OF node of the PCI controller when
looking it up.

quoted

I don't see any reason why PPC wouldn't benefit from this
series.

It's not clear to me what the benefit of this is at all, much less for PPC.
What is the fundamental problem with deferred probes?  In the cover letter
you say this change saves 2.3 seconds, but where is that time being consumed?
 Are the drivers taking too long in their probe function trying to initialize
and then deferring, rather than checking for dependencies up front?  Or are
there really so many devices and such a pessimal ordering that most of the
time is spent iterating through and reordering the list, with each defer
happening quickly?

The problem is that a device that defers its probe is currently sent
to the back of the queue, and that's undesired in some use cases in
which there's a device that should be up as soon as possible during
boot (and boot takes a long time). So the goal is to change the order
in which devices with dependencies end up probing.

Even if something different does need to be done at this level, forcing all
OF platform devices to be probed at the late_initcall level seems quite
intrusive.  You limited it to OF because people complained that other things
will break.  Things still broke.  Surely there's a better way to address the
problem.  Can't the delay be requested by drivers that might otherwise need
to defer (which could be done incrementally, focusing on the worst
performance problems), rather than enabling it for everything?

Yes, given the amount of breakage that's a sensible option. But in any
case and even if this series is most likely to be dropped, I recommend
to make explicit as many implicit dependencies as possible.

Regards,

Tomeu

-Scott


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