On Thu, Aug 21, 2025 at 12:09:44AM +0800, Hans Zhang wrote:
> The msleep(2) may sleep up to 20ms due to timer granularity, which can
> cause unnecessary delays. According to PCI spec v3.0 7.6.4.2, the minimum
> Trst is 1ms and we doubled that to 2ms to meet the requirement. Using
> usleep_range(2000, 2001) provides a more precise delay of exactly 2ms.
> ...
Please cite a recent spec version, i.e., r7.0. I see this probably
came from the comment at the change; I wouldn't object to updating
the comment, too.
> WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
> #4630: FILE: drivers/pci/pci.c:4630:
> + msleep(1);
> ...
> WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
> #3970: FILE: drivers/pci/quirks.c:3970:
> + msleep(10);
> +++ b/drivers/pci/pci.c
> @@ -4967,7 +4967,7 @@ void pci_reset_secondary_bus(struct pci_dev *dev)
> * PCI spec v3.0 7.6.4.2 requires minimum Trst of 1ms. Double
> * this to 2ms to ensure that we meet the minimum requirement.
> */
> - msleep(2);
> + usleep_range(2000, 2001);
IMO the most valuable thing here would be to replace the hard-coded
"2" with some kind of #define explicitly tied to the spec. Similarly
for the other cases.
There is some concern [1] about places that say "msleep(1)" but
actually rely on the current behavior of a longer sleep.
Apart from that concern, I think fsleep() would be my first choice.
usleep_range(x, x+1) defeats the purpose of the range, which is to
reduce interrupts; see 5e7f5a178bba ("timer: Added usleep_range
timer").
Bjorn
[1] https://lore.kernel.org/all/20070809001640.ec2f3bfb.akpm@xxxxxxxxxxxxxxxxxxxx/
