PCI/PM: Elevate PM usage during reset probing

[PATCH 0/2] PCI/PM: Elevate PM usage during reset probing

Posted by Alex Williamson 9 months, 2 weeks ago

I encountered a confusing scenario where a device reports NoSoftRst- and
doesn't have any associated quirks to set PCI_DEV_FLAGS_NO_PM_RESET, but
it refuses to probe for PM reset support using the sysfs reset_method
attribute.  The reason turns out to be that we don't increment the usage
count while probing, the driver has the device in D3, where this system
seems to support D3cold, and the PM control register is read back as
0xffff.

The cleanup __free helper seems to be the cleanest solution here, versus
refactoring to a common exit point or wrappers around reset_fn, but feel
free to suggest otherwise.  I see a couple potential other use cases for
this helper in the vfio code.

Please review.  Thanks,

Alex

Alex Williamson (2):
  PM: runtime: Define pm_runtime_put cleanup helper
  PCI: Increment PM usage counter when probing reset methods

 drivers/pci/pci-sysfs.c    | 3 +++
 include/linux/pm_runtime.h | 2 ++
 2 files changed, 5 insertions(+)

-- 
2.48.1

Re: [PATCH 0/2] PCI/PM: Elevate PM usage during reset probing

Posted by Bjorn Helgaas 9 months, 2 weeks ago

On Tue, Apr 22, 2025 at 05:05:30PM -0600, Alex Williamson wrote:
> I encountered a confusing scenario where a device reports NoSoftRst- and
> doesn't have any associated quirks to set PCI_DEV_FLAGS_NO_PM_RESET, but
> it refuses to probe for PM reset support using the sysfs reset_method
> attribute.  The reason turns out to be that we don't increment the usage
> count while probing, the driver has the device in D3, where this system
> seems to support D3cold, and the PM control register is read back as
> 0xffff.
> 
> The cleanup __free helper seems to be the cleanest solution here, versus
> refactoring to a common exit point or wrappers around reset_fn, but feel
> free to suggest otherwise.  I see a couple potential other use cases for
> this helper in the vfio code.
> 
> Please review.  Thanks,
> 
> Alex
> 
> Alex Williamson (2):
>   PM: runtime: Define pm_runtime_put cleanup helper
>   PCI: Increment PM usage counter when probing reset methods
> 
>  drivers/pci/pci-sysfs.c    | 3 +++
>  include/linux/pm_runtime.h | 2 ++
>  2 files changed, 5 insertions(+)

Applied to pci/pm for v6.16, thanks, Alex!