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

On Mon, Sep 08, 2025 at 07:39:07AM -0500, Mario Limonciello wrote:

On 9/8/25 4:19 AM, Greg Kroah-Hartman wrote:

quoted

On Sat, Sep 06, 2025 at 09:36:31AM -0500, Mario Limonciello (AMD) wrote:

quoted

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 <redacted>
Cc: Eric Naim <redacted>
---
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.

quoted

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.

This second one is probably the best.  A new command line is not going
to probably be used and just be a pain to maintain over time.

thanks,

greg k-h