linux-kernel - Re: [PATCH v3] PCI/PM: Switch D3Hot delay to also use usleep

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Date:   Wed, 17 Aug 2022 17:27:00 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Will McVicker <willmcvicker@...gle.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, kernel-team@...roid.com,
        Sajid Dalvi <sdalvi@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PCI/PM: Switch D3Hot delay to also use usleep_range

On Wed, Aug 17, 2022 at 11:08:21PM +0000, Will McVicker wrote:
> From: Sajid Dalvi <sdalvi@...gle.com>
> 
> Since the PCI spec requires a 10ms D3Hot delay (defined by
> PCI_PM_D3HOT_WAIT) and a few of the PCI quirks update the D3Hot delay up
> to 120ms, let's add support for both usleep_range and msleep based on
> the delay time to improve the delay accuracy.
> 
> This patch is based off of a commit from Sajid Dalvi <sdalvi@...gle.com>
> in the Pixel 6 kernel tree [1]. Testing on a Pixel 6, found that the
> 10ms delay for the Exynos PCIe device was on average delaying for 19ms
> when the spec requires 10ms. Switching from msleep to uslseep_range
> therefore decreases the resume time on a Pixel 6 on average by 9ms.
> 
> [1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3
> 
> Signed-off-by: Sajid Dalvi <sdalvi@...gle.com>
> Signed-off-by: Will McVicker <willmcvicker@...gle.com>

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>