Re: [PATCH] PCI/ASPM: Add back L1 PM Substate save and restore

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Jun 28, 2023 at 01:59:40PM +0300, Mika Westerberg wrote:
> Hi Thomas,
> 
> On Wed, Jun 28, 2023 at 12:24:06PM +0200, Thomas Witt wrote:
> > On 28/06/2023 08:46, Mika Westerberg wrote:
> > > @Thomas, is there any particular reason you have this option in the
> > > command line? There is possibility that S3 is not even fully validated
> > > if the system advertises S0 low power sleep instead.
> > 
> > In fact, there is: Entering suspend-to-ram without setting
> > /sys/power/mem_sleep to "deep", my laptop consumes about the same power as
> > it would idling online. The manufacturer suggests setting that commandline
> > parameter:
> > 
> > <https://www.tuxedocomputers.com/en/Infos/Help-Support/Instructions/Fine-tuning-of-power-management-with-suspend-standby.tuxedo#>
> 
> Thanks for the clarification.
> 
> > I just retested your patch with setting mem_sleep to "s2idle", and it no
> > longer triggers the loss of PCI devices. I guess that could be the indicator
> > that Björn asked for.
> 
> I wonder if the patch actually helps here now because the reason we want
> to add it back is that it allows the CPU to enter lower power states and
> thus reducing the power consumption in S2idle too. Do you observe that
> when you have the patch applied?

One possibility is to check the package C-state residency like:

  # cat /sys/kernel/debug/pmc_core/package_cstate_show

after system sleep and see if there is a change with the patch applied,
as done here:

  https://bugzilla.kernel.org/show_bug.cgi?id=217321