linux-kernel - Re: [PATCH] PCI/PM: Avoid redundant delays on D3hot->D3cold

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Message-ID: <aSXXUmfy77ZAiShd@google.com>
Date: Tue, 25 Nov 2025 08:20:34 -0800
From: Brian Norris <briannorris@...omium.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] PCI/PM: Avoid redundant delays on D3hot->D3cold

On Fri, Oct 03, 2025 at 03:40:09PM -0700, Brian Norris wrote:
> From: Brian Norris <briannorris@...gle.com>
> 
> When transitioning to D3cold, __pci_set_power_state() will first
> transition a device to D3hot. If the device was already in D3hot, this
> will add excess work:
> (a) read/modify/write PMCSR; and
> (b) excess delay (pci_dev_d3_sleep()).
> 
> For (b), we already performed the necessary delay on the previous D3hot
> entry; this was extra noticeable when evaluating runtime PM transition
> latency.
> 
> Check whether we're already in the target state before continuing.
> 
> Note that __pci_set_power_state() already does this same check for other
> state transitions, but D3cold is special because __pci_set_power_state()
> converts it to D3hot for the purposes of PMCSR.
> 
> This seems to be an oversight in commit 0aacdc957401 ("PCI/PM: Clean up
> pci_set_low_power_state()").
> 
> Fixes: 0aacdc957401 ("PCI/PM: Clean up pci_set_low_power_state()")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Brian Norris <briannorris@...gle.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>

I'd like to know the status of this patch, with the merge window
approaching. It sounds like people agreed it fixes a confirmed
regression. I also don't think the request to remove all power state
management from all drivers was a reasonable one.

Brian