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Wysocki" , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] PCI/PM: Avoid redundant delays on D3hot->D3cold Message-ID: References: <20251003154008.1.I7a21c240b30062c66471329567a96dceb6274358@changeid> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251003154008.1.I7a21c240b30062c66471329567a96dceb6274358@changeid> On Fri, Oct 03, 2025 at 03:40:09PM -0700, Brian Norris wrote: > From: Brian Norris > > 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: > Signed-off-by: Brian Norris > Signed-off-by: Brian Norris 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