Re: [PATCH v3] PCI/PM: Switch D3Hot delay to also use usleep_range

From: William McVicker
Date: Mon Aug 29 2022 - 14:08:59 EST


On 08/17/2022, Will McVicker wrote:
> From: Sajid Dalvi <sdalvi@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Will McVicker <willmcvicker@xxxxxxxxxx>
> ---
> 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