PCI/PM: Reduce D3hot delay with usleep_range()

PCIe r6.0, sec 5.9, requires a 10ms delay between programming a device to
change to or from D3hot and the time the device is next accessed (unless
Readiness Notifications are used).

The 10ms value (PCI_PM_D3HOT_WAIT) doesn't appear directly here because
some chipsets require 120ms for devices *below* them (pci_pm_d3hot_delay)
and some devices require more or less than 10ms (dev->d3hot_delay).

But msleep(10) typically waits about *20*ms, which is more than we need.
Switch to usleep_range() to improve the delay accuracy.

Based on a commit from Sajid in the Pixel 6 kernel tree [1].  On a Pixel 6,
the 10ms delay for the Exynos PCIe device delayed for an average of 19ms.
Switching to usleep_range() decreased the resume time by about 9ms.

[1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3

[bhelgaas commit log, add timers-howto.rst link]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/timers/timers-howto.rst?id=v5.19#n73
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sajid Dalvi <[email protected]>
Signed-off-by: Will McVicker <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Matthias Kaehlcke <[email protected]>

Author: Sajid Dalvi

drivers/pci/pci.c

@@ -66,13 +66,15 @@ struct pci_pme_device {
 
 static void pci_dev_d3_sleep(struct pci_dev *dev)
 {
-	unsigned int delay = dev->d3hot_delay;
-
-	if (delay < pci_pm_d3hot_delay)
-		delay = pci_pm_d3hot_delay;
-
-	if (delay)
-		msleep(delay);
+	unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay);
+	unsigned int upper;
+
+	if (delay_ms) {
+		/* Use a 20% upper bound, 1ms minimum */
+		upper = max(DIV_ROUND_CLOSEST(delay_ms, 5), 1U);
+		usleep_range(delay_ms * USEC_PER_MSEC,
+			     (delay_ms + upper) * USEC_PER_MSEC);
+	}
 }
 
 bool pci_reset_supported(struct pci_dev *dev)