linux-kernel - Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

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Message-ID: <20240915071406.GR275077@black.fi.intel.com>
Date: Sun, 15 Sep 2024 10:14:06 +0300
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Kai-Heng Feng <kaihengfeng@...il.com>,
	Bjorn Helgaas <helgaas@...nel.org>, bhelgaas@...gle.com,
	linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

Hi,

On Fri, Sep 13, 2024 at 03:33:33PM -0500, Mario Limonciello wrote:
> > I know this is about entering S5 (power off) but I wonder if simply
> > disabling the device (I/O, MMIO and bus mastering) could stop it from
> > waking up?
> 
> To me, it's a two-fold problem.  The device consumes too much power, and the
> device issues interrupts when system is in S5.
> 
> Putting it in D3 should nip both, disabling the device might help the
> latter.
> 
> I did the same thing a vendor did for KH where I double checked the waveform
> at S5 and could see the devices still in D0.
> 
> Or do you think that by the device being in D0 but disabled should be enough
> for decreasing power?

No, not about power but just to solve the issue here. I'm not objecting
putting the device into D3 instead on the grounds that if Windows does
this then probably it is safe or us to do as well and also avoids
possible untested paths in the firmware side too.

Strictly based on ACPI spec [1] there is no such requirement though.

[1] https://uefi.org/specs/ACPI/6.5/16_Waking_and_Sleeping.html#transitioning-from-the-working-to-the-soft-off-state