linux-kernel - [PATCH v3 1/2] PCI: Add flr_delay parameter to pci

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Message-Id: <20250611000552.1989795-2-grwhyte@linux.microsoft.com>
Date: Wed, 11 Jun 2025 00:05:51 +0000
From: grwhyte@...ux.microsoft.com
To: linux-pci@...r.kernel.org
Cc: shyamsaini@...ux.microsoft.com,
	code@...icks.com,
	Okaya@...nel.org,
	bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/2] PCI: Add flr_delay parameter to pci_dev struct

From: Graham Whyte <grwhyte@...ux.microsoft.com>

Add a new flr_delay member of the pci_dev struct to allow customization of
the delay after FLR for devices that do not support immediate readiness.

Signed-off-by: Graham Whyte <grwhyte@...ux.microsoft.com>
---
 drivers/pci/pci.c   | 8 ++++++--
 drivers/pci/pci.h   | 2 ++
 include/linux/pci.h | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e9448d55113b..04f2660df7c4 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3233,6 +3233,8 @@ void pci_pm_init(struct pci_dev *dev)
 	dev->bridge_d3 = pci_bridge_d3_possible(dev);
 	dev->d3cold_allowed = true;
 
+	dev->flr_delay = PCI_FLR_DELAY;
+
 	dev->d1_support = false;
 	dev->d2_support = false;
 	if (!pci_no_d1d2(dev)) {
@@ -4529,9 +4531,11 @@ int pcie_flr(struct pci_dev *dev)
 	/*
 	 * Per PCIe r4.0, sec 6.6.2, a device must complete an FLR within
 	 * 100ms, but may silently discard requests while the FLR is in
-	 * progress.  Wait 100ms before trying to access the device.
+	 * progress.  Wait 100ms before trying to access the device, unless
+	 * otherwise modified if the device supports a faster reset.
+	 * Use usleep_range to support delays under 20ms.
 	 */
-	msleep(100);
+	usleep_range(dev->flr_delay, dev->flr_delay+1);
 
 	return pci_dev_wait(dev, "FLR", PCIE_RESET_READY_POLL_MS);
 }
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 12215ee72afb..abc1cf6e6d9b 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -135,6 +135,8 @@ struct pci_cap_saved_state *pci_find_saved_ext_cap(struct pci_dev *dev,
 #define PCI_PM_D3HOT_WAIT       10	/* msec */
 #define PCI_PM_D3COLD_WAIT      100	/* msec */
 
+#define PCI_FLR_DELAY           100000 /* usec */
+
 void pci_update_current_state(struct pci_dev *dev, pci_power_t state);
 void pci_refresh_power_state(struct pci_dev *dev);
 int pci_power_up(struct pci_dev *dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f392..4c9989037ed1 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -402,6 +402,7 @@ struct pci_dev {
 						   bit manually */
 	unsigned int	d3hot_delay;	/* D3hot->D0 transition time in ms */
 	unsigned int	d3cold_delay;	/* D3cold->D0 transition time in ms */
+	unsigned int    flr_delay;      /* pci post flr sleep time in us */
 
 	u16		l1ss;		/* L1SS Capability pointer */
 #ifdef CONFIG_PCIEASPM
-- 
2.25.1