linux-kernel - [PATCH] PCI: Replace msleep(2) with usleep

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Message-Id: <20250820160944.489061-1-18255117159@163.com>
Date: Thu, 21 Aug 2025 00:09:44 +0800
From: Hans Zhang <18255117159@....com>
To: bhelgaas@...gle.com,
	helgaas@...nel.org,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Hans Zhang <18255117159@....com>
Subject: [PATCH] PCI: Replace msleep(2) with usleep_range() for precise delay

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.

Signed-off-by: Hans Zhang <18255117159@....com>
---
Dear maintainers,

During the development process, I often check whether the file encoding meets the
basic rules. A warning appears when checking the following files:

./scripts/checkpatch.pl --no-tree --show-types --ignore EMAIL_SUBJECT,FILE_PATH_CHANGES,\
GERRIT_CHANGE_ID,UNDOCUMENTED_DT_STRING,TYPO_SPELLING -f drivers/pci/pci.c

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#4914: FILE: drivers/pci/pci.c:4914:
+	msleep(2);


In addition, I also found that the following documents all have similar problems.
Here, I'll first submit a patch to ask everyone. If it's necessary, I'll continue
to submit related patches later. If not, please ignore it.

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().
#342: FILE: drivers/pci/controller/pcie-rcar-host.c:342:
+		msleep(1);

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#1368: FILE: drivers/pci/controller/pcie-brcmstb.c:1368:
+		msleep(5);

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#42: FILE: drivers/pci/controller/pcie-rcar.c:42:
+		msleep(5);

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#106: FILE: drivers/pci/hotplug/pciehp_hpc.c:106:
+		msleep(10);
WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#286: FILE: drivers/pci/hotplug/pciehp_hpc.c:286:
+		msleep(10);

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#138: FILE: drivers/pci/pcie/dpc.c:138:
+		msleep(10);

WARNING:MSLEEP: msleep < 20ms can sleep for up to 20ms; see function description of msleep().
#3970: FILE: drivers/pci/quirks.c:3970:
+		msleep(10);
---
 drivers/pci/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b0f4d98036cd..ffe491635144 100644
--- a/drivers/pci/pci.c
+++ 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);
 
 	ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
 	pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl);

base-commit: b19a97d57c15643494ac8bfaaa35e3ee472d41da
-- 
2.25.1