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

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Date:   Mon, 29 Aug 2022 18:08:47 +0000
From:   William McVicker <willmcvicker@...gle.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     kernel-team@...roid.com, Sajid Dalvi <sdalvi@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        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 08/17/2022, 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>
> ---
>  drivers/pci/pci.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> v3:
>  * Use DIV_ROUND_CLOSEST instead of bit manipulation.
>  * Minor refactor to use max() where relavant.
> 
> v2:
>  * Update to use 20-25% upper bound
>  * Update to use usleep_range() for <=20ms, else use msleep()
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95bc329e74c0..cfa8386314f2 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -66,13 +66,19 @@ struct pci_pme_device {
>  
>  static void pci_dev_d3_sleep(struct pci_dev *dev)
>  {
> -	unsigned int delay = dev->d3hot_delay;
> +	unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay);
>  
> -	if (delay < pci_pm_d3hot_delay)
> -		delay = pci_pm_d3hot_delay;
> +	if (delay_ms) {
> +		if (delay_ms <= 20) {
> +			/* Use a 20% upper bound with 1ms minimum */
> +			unsigned int upper = max(DIV_ROUND_CLOSEST(delay_ms, 5), 1U);
>  
> -	if (delay)
> -		msleep(delay);
> +			usleep_range(delay_ms * USEC_PER_MSEC,
> +				     (delay_ms + upper) * USEC_PER_MSEC);
> +		} else {
> +			msleep(delay_ms);
> +		}
> +	}
>  }
>  
>  bool pci_reset_supported(struct pci_dev *dev)
> 
> base-commit: 274a2eebf80c60246f9edd6ef8e9a095ad121264
> -- 
> 2.37.1.595.g718a3a8f04-goog
> 

Hi Bjorn,

I'm just checking up on this patch in case it got lost in your inbox. Please
take a look and let me know if you have any concerns.

And thanks again for the reviews Matthias!

Regards,
Will