[PATCH 4/4] PCI/sysfs: Allow userspace to query and set device reset mechanism

[ameynarkhede03@gmail.com]

From: Amey Narkhede <ameynarkhede03@gmail.com>

Add reset_methods_enabled bitmap to struct pci_dev to
keep track of user preferred device reset mechanisms.
Add reset_method sysfs attribute to query and set
user preferred device reset mechanisms.

Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
---
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

 Documentation/ABI/testing/sysfs-bus-pci | 15 ++++++
 drivers/pci/pci-sysfs.c                 | 66 +++++++++++++++++++++++--
 drivers/pci/pci.c                       |  3 +-
 include/linux/pci.h                     |  2 +
 4 files changed, 82 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 25c9c3977..ae53ecd2e 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -121,6 +121,21 @@ Description:
 		child buses, and re-discover devices removed earlier
 		from this part of the device tree.

+What:		/sys/bus/pci/devices/.../reset_method
+Date:		March 2021
+Contact:	Amey Narkhede <ameynarkhede03@gmail.com>
+Description:
+		Some devices allow an individual function to be reset
+		without affecting other functions in the same slot.
+		For devices that have this support, a file named reset_method
+		will be present in sysfs. Reading this file will give names
+		of the device supported reset methods. Currently used methods
+		are enclosed in brackets. Writing the name of any of the device
+		supported reset method to this file will set the reset method to
+		be used when resetting the device. Writing "none" to this file
+		will disable ability to reset the device and writing "default"
+		will return to the original value.
+
 What:		/sys/bus/pci/devices/.../reset
 Date:		July 2009
 Contact:	Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 78d2c130c..3cd06d1c0 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1304,6 +1304,59 @@ static const struct bin_attribute pcie_config_attr = {
 	.write = pci_write_config,
 };

+static ssize_t reset_method_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	const struct pci_reset_fn_method *reset;
+	struct pci_dev *pdev = to_pci_dev(dev);
+	ssize_t len = 0;
+	int i;
+
+	for (i = 0, reset = pci_reset_fn_methods; reset->reset_fn; i++, reset++) {
+		if (pdev->reset_methods_enabled & (1 << i))
+			len += sysfs_emit_at(buf, len, "[%s] ", reset->name);
+		else if (pdev->reset_methods & (1 << i))
+			len += sysfs_emit_at(buf, len, "%s ", reset->name);
+	}
+
+	return len;
+}
+
+static ssize_t reset_method_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	const struct pci_reset_fn_method *reset = pci_reset_fn_methods;
+	struct pci_dev *pdev = to_pci_dev(dev);
+	u8 reset_mechanism;
+	int i = 0;
+
+	/* Writing none disables reset */
+	if (sysfs_streq(buf, "none")) {
+		reset_mechanism = 0;
+	} else if (sysfs_streq(buf, "default")) {
+		/* Writing default returns to initial value */
+		reset_mechanism = pdev->reset_methods;
+	} else {
+		reset_mechanism = 0;
+		for (; reset->reset_fn; i++, reset++) {
+			if (sysfs_streq(buf, reset->name)) {
+				reset_mechanism = 1 << i;
+				break;
+			}
+		}
+		if (!reset_mechanism || !(pdev->reset_methods & reset_mechanism))
+			return -EINVAL;
+	}
+
+	pdev->reset_methods_enabled = reset_mechanism;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(reset_method);
+
 static ssize_t reset_store(struct device *dev, struct device_attribute *attr,
 			   const char *buf, size_t count)
 {
@@ -1337,11 +1390,16 @@ static int pci_create_capabilities_sysfs(struct pci_dev *dev)
 	if (dev->reset_methods) {
 		retval = device_create_file(&dev->dev, &dev_attr_reset);
 		if (retval)
-			goto error;
+			goto err_reset;
+		retval = device_create_file(&dev->dev, &dev_attr_reset_method);
+		if (retval)
+			goto err_method;
 	}
 	return 0;

-error:
+err_method:
+	device_remove_file(&dev->dev, &dev_attr_reset);
+err_reset:
 	pcie_vpd_remove_sysfs_dev_files(dev);
 	return retval;
 }
@@ -1417,8 +1475,10 @@ int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
 static void pci_remove_capabilities_sysfs(struct pci_dev *dev)
 {
 	pcie_vpd_remove_sysfs_dev_files(dev);
-	if (dev->reset_methods)
+	if (dev->reset_methods) {
 		device_remove_file(&dev->dev, &dev_attr_reset);
+		device_remove_file(&dev->dev, &dev_attr_reset_method);
+	}
 }

 /**
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b7f6c6588..81cebea56 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5106,7 +5106,7 @@ int __pci_reset_function_locked(struct pci_dev *dev)
 	might_sleep();

 	for (i = 0, reset = pci_reset_fn_methods; reset->reset_fn; i++, reset++) {
-		if (!(dev->reset_methods & (1 << i)))
+		if (!(dev->reset_methods_enabled & (1 << i)))
 			continue;

 		/*
@@ -5153,6 +5153,7 @@ void pci_init_reset_methods(struct pci_dev *dev)
 		else if (rc != -ENOTTY)
 			break;
 	}
+	dev->reset_methods_enabled = dev->reset_methods;
 }

 /**
diff --git a/include/linux/pci.h b/include/linux/pci.h
index a2f003f4e..400f614e0 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -335,6 +335,8 @@ struct pci_dev {
 	 * See pci_reset_fn_methods array in pci.c
 	 */
 	u8 __bitwise reset_methods;		/* bitmap for device supported reset capabilities */
+	/* bitmap for user enabled and device supported reset capabilities */
+	u8 __bitwise reset_methods_enabled;
 #ifdef CONFIG_PCIEAER
 	u16		aer_cap;	/* AER capability offset */
 	struct aer_stats *aer_stats;	/* AER stats for this device */
--
2.30.2