[PATCHv2 1/2] pci: provide bus reset attribute

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Resetting a bus from an end device only works if it's the only function
on or below that bus.

Provide an attribute on the pci_dev bridge device that can perform the
secondary bus reset. This makes it possible for a user to safely reset
multiple devices in a single command using the secondary bus reset
action.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
v1->v2:

  Moved the attribute from the pci_bus to the bridge's pci_dev

  And renamed it to "reset_subordinate" to distinguish from other
  existing device "reset" attributes.

  Added documentation.

  Follow up patch to warn if the action was potentially harmful.

 Documentation/ABI/testing/sysfs-bus-pci | 11 +++++++++++
 drivers/pci/pci-sysfs.c                 | 23 +++++++++++++++++++++++
 drivers/pci/pci.c                       |  2 +-
 drivers/pci/pci.h                       |  1 +
 4 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 7f63c7e977735..5da6a14dc326b 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -163,6 +163,17 @@ Description:
 		will be present in sysfs.  Writing 1 to this file
 		will perform reset.
 
+What:		/sys/bus/pci/devices/.../reset_subordinate
+Date:		October 2024
+Contact:	linux-pci@vger.kernel.org
+Description:
+		This is visible only for bridge devices. If you want to reset
+		all devices attached through the subordinate bus of a specific
+		bridge device, writing 1 to this will try to do it.  This will
+		affect all devices attached to the system through this bridge
+		similiar to writing 1 to their individual "reset" file, so use
+		with caution.
+
 What:		/sys/bus/pci/devices/.../vpd
 Date:		February 2008
 Contact:	Ben Hutchings <bwh@kernel.org>
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 5d0f4db1cab78..480a99e50612b 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -521,6 +521,28 @@ static ssize_t bus_rescan_store(struct device *dev,
 static struct device_attribute dev_attr_bus_rescan = __ATTR(rescan, 0200, NULL,
 							    bus_rescan_store);
 
+static ssize_t reset_subordinate_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	struct pci_bus *bus = pdev->subordinate;
+	unsigned long val;
+
+	if (kstrtoul(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (val) {
+		int ret = __pci_reset_bus(bus);
+
+		if (ret)
+			return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(reset_subordinate);
+
 #if defined(CONFIG_PM) && defined(CONFIG_ACPI)
 static ssize_t d3cold_allowed_store(struct device *dev,
 				    struct device_attribute *attr,
@@ -625,6 +647,7 @@ static struct attribute *pci_dev_attrs[] = {
 static struct attribute *pci_bridge_attrs[] = {
 	&dev_attr_subordinate_bus_number.attr,
 	&dev_attr_secondary_bus_number.attr,
+	&dev_attr_reset_subordinate.attr,
 	NULL,
 };
 
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7d85c04fbba2a..338dfcd983f1e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5880,7 +5880,7 @@ EXPORT_SYMBOL_GPL(pci_probe_reset_bus);
  *
  * Same as above except return -EAGAIN if the bus cannot be locked
  */
-static int __pci_reset_bus(struct pci_bus *bus)
+int __pci_reset_bus(struct pci_bus *bus)
 {
 	int rc;
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 14d00ce45bfa9..1cdc2c9547a7e 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -104,6 +104,7 @@ bool pci_reset_supported(struct pci_dev *dev);
 void pci_init_reset_methods(struct pci_dev *dev);
 int pci_bridge_secondary_bus_reset(struct pci_dev *dev);
 int pci_bus_error_reset(struct pci_dev *dev);
+int __pci_reset_bus(struct pci_bus *bus);
 
 struct pci_cap_saved_data {
 	u16		cap_nr;
-- 
2.43.5