Re: [PATCH v6 RESEND 00/11] Improvements to S5 power consumption

[Mario Limonciello <superm1@kernel.org>]

On 9/8/25 4:19 AM, Greg Kroah-Hartman wrote:
> On Sat, Sep 06, 2025 at 09:36:31AM -0500, Mario Limonciello (AMD) wrote:
>> A variety of issues both in function and in power consumption have been
>> raised as a result of devices not being put into a low power state when
>> the system is powered off.
>>
>> There have been some localized changes[1] to PCI core to help these issues,
>> but they have had various downsides.
>>
>> This series instead tries to use the S4 flow when the system is being
>> powered off.  This lines up the behavior with what other operating systems
>> do as well.  If for some reason that fails or is not supported, run their
>> shutdown() callbacks.
>>
>> Cc: AceLan Kao <acelan.kao@canonical.com>
>> Cc: Kai-Heng Feng <kaihengf@nvidia.com>
>> Cc: Mark Pearson <mpearson-lenovo@squebb.ca>
>> Cc: Merthan Karakaş <m3rthn.k@gmail.com>
>> Cc: Eric Naim <dnaim@cachyos.org>
>> ---
>> v6 RESEND:
>>   * Resent because Greg said he was ignoring it and would like the whole
>>     series to be able to review.
> 
> Messy, but wow, I'll trust you all that this actually works properly.

Yes; I double checked from a UART log all devices (now) went to correct 
state and from power measurement hardware the respective drop in power.

I will note I have a sampling bias of hardware being x86 AMD hardware.
Some of the testers of the series also tested Intel hardware which had 
similar power consumption problem, and I know there were improvements 
there too.

We probably will have to wait for linux-next for non-x86 hardware coverage.
> No objections from me, but I don't want my ack on this as I don't know
> how to maintain it :)
> 

I mean - if all goes well even a failed S4 flow should fall back to old 
path shutdown.  I *did contrive some failures* in an earlier version of 
the series and confirmed in the UART log it emitted the printk that it 
was falling back to shutdown.

I had two ideas that maybe could help for regression risk though:
1) I could add a shutdown= kernel parameter.  I'm not sure what words to 
use for the two paths but the idea would be if someone had a shutdown 
failure they could isolate if it's due to this by adding the parameter.

2) I could make a Documentation/ file explaining some examples how to 
get the shutdown log saved to pstore in case they don't have a UART 
available.