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SubjectRe: [PATCH v2] PCI/PM: Switch D3Hot delay to also use usleep_range
Hi Will,

On Wed, Aug 17, 2022 at 06:52:02PM +0000, Will McVicker wrote:
> From: Sajid Dalvi <sdalvi@google.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@google.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@google.com>
> Signed-off-by: Will McVicker <willmcvicker@google.com>
> ---
> drivers/pci/pci.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95bc329e74c0..97a042ca9032 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -63,16 +63,26 @@ struct pci_pme_device {
> };
>
> #define PME_TIMEOUT 1000 /* How long between PME checks */
> +#define MAX(a, b) ((a) >= (b) ? (a) : (b))

no need to define this macro, you can use max() from
include/linux/minmax.h instead.

>
> static void pci_dev_d3_sleep(struct pci_dev *dev)
> {
> - unsigned int delay = dev->d3hot_delay;
> + unsigned int delay_ms = dev->d3hot_delay;
>
> - if (delay < pci_pm_d3hot_delay)
> - delay = pci_pm_d3hot_delay;
> + if (delay_ms < pci_pm_d3hot_delay)
> + delay_ms = pci_pm_d3hot_delay;

nit: since you are already touching this code you could change it to:

unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay);

>
> - if (delay)
> - msleep(delay);
> + if (delay_ms) {
> + if (delay_ms <= 20) {
> + /* Use a 20-25% upper bound with 1ms minimum */
> + unsigned int upper = MAX((delay_ms >> 3) << 1, 1);

Not sure this optimization of using bit shifts instead of the clearer do_div()
is really needed here. pci_dev_d3_sleep() is not a super hot code path IIUC.

> +
> + 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
>

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