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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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