PCI: Allow userspace to query and set device reset mechanism

Add "reset_method" sysfs attribute to enable user to query and set
preferred device reset methods and their ordering.

[bhelgaas: on invalid sysfs input, return error and preserve previous
config, as in earlier patch versions]
Co-developed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/r/20210817180500.1253-6-ameynarkhede03@gmail.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>

Documentation/ABI/testing/sysfs-bus-pci

@@ -121,6 +121,23 @@ Description:
 		child buses, and re-discover devices removed earlier
 		from this part of the device tree.
 
+What:		/sys/bus/pci/devices/.../reset_method
+Date:		August 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 is present in sysfs.  Reading this file
+		gives names of the supported and enabled reset methods and
+		their ordering.  Writing a space-separated list of names of
+		reset methods sets the reset methods and ordering to be
+		used when resetting the device.  Writing an empty string
+		disables the ability to reset the device.  Writing
+		"default" enables all supported reset methods in the
+		default ordering.
+
 What:		/sys/bus/pci/devices/.../reset
 Date:		July 2009
 Contact:	Michael S. Tsirkin <mst@redhat.com>

drivers/pci/pci-sysfs.c

@@ -1491,6 +1491,7 @@ const struct attribute_group *pci_dev_groups[] = {
 	&pci_dev_config_attr_group,
 	&pci_dev_rom_attr_group,
 	&pci_dev_reset_attr_group,
+	&pci_dev_reset_method_attr_group,
 	&pci_dev_vpd_attr_group,
 #ifdef CONFIG_DMI
 	&pci_dev_smbios_attr_group,

drivers/pci/pci.c

@@ -5132,6 +5132,128 @@ static const struct pci_reset_fn_method pci_reset_fn_methods[] = {
 	{ pci_reset_bus_function, .name = "bus" },
 };
 
+static ssize_t reset_method_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	ssize_t len = 0;
+	int i, m;
+
+	for (i = 0; i < PCI_NUM_RESET_METHODS; i++) {
+		m = pdev->reset_methods[i];
+		if (!m)
+			break;
+
+		len += sysfs_emit_at(buf, len, "%s%s", len ? " " : "",
+				     pci_reset_fn_methods[m].name);
+	}
+
+	if (len)
+		len += sysfs_emit_at(buf, len, "\n");
+
+	return len;
+}
+
+static int reset_method_lookup(const char *name)
+{
+	int m;
+
+	for (m = 1; m < PCI_NUM_RESET_METHODS; m++) {
+		if (sysfs_streq(name, pci_reset_fn_methods[m].name))
+			return m;
+	}
+
+	return 0;	/* not found */
+}
+
+static ssize_t reset_method_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	char *options, *name;
+	int m, n;
+	u8 reset_methods[PCI_NUM_RESET_METHODS] = { 0 };
+
+	if (sysfs_streq(buf, "")) {
+		pdev->reset_methods[0] = 0;
+		pci_warn(pdev, "All device reset methods disabled by user");
+		return count;
+	}
+
+	if (sysfs_streq(buf, "default")) {
+		pci_init_reset_methods(pdev);
+		return count;
+	}
+
+	options = kstrndup(buf, count, GFP_KERNEL);
+	if (!options)
+		return -ENOMEM;
+
+	n = 0;
+	while ((name = strsep(&options, " ")) != NULL) {
+		if (sysfs_streq(name, ""))
+			continue;
+
+		name = strim(name);
+
+		m = reset_method_lookup(name);
+		if (!m) {
+			pci_err(pdev, "Invalid reset method '%s'", name);
+			goto error;
+		}
+
+		if (pci_reset_fn_methods[m].reset_fn(pdev, 1)) {
+			pci_err(pdev, "Unsupported reset method '%s'", name);
+			goto error;
+		}
+
+		if (n == PCI_NUM_RESET_METHODS - 1) {
+			pci_err(pdev, "Too many reset methods\n");
+			goto error;
+		}
+
+		reset_methods[n++] = m;
+	}
+
+	reset_methods[n] = 0;
+
+	/* Warn if dev-specific supported but not highest priority */
+	if (pci_reset_fn_methods[1].reset_fn(pdev, 1) == 0 &&
+	    reset_methods[0] != 1)
+		pci_warn(pdev, "Device-specific reset disabled/de-prioritized by user");
+	memcpy(pdev->reset_methods, reset_methods, sizeof(pdev->reset_methods));
+	kfree(options);
+	return count;
+
+error:
+	/* Leave previous methods unchanged */
+	kfree(options);
+	return -EINVAL;
+}
+static DEVICE_ATTR_RW(reset_method);
+
+static struct attribute *pci_dev_reset_method_attrs[] = {
+	&dev_attr_reset_method.attr,
+	NULL,
+};
+
+static umode_t pci_dev_reset_method_attr_is_visible(struct kobject *kobj,
+						    struct attribute *a, int n)
+{
+	struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
+
+	if (!pci_reset_supported(pdev))
+		return 0;
+
+	return a->mode;
+}
+
+const struct attribute_group pci_dev_reset_method_attr_group = {
+	.attrs = pci_dev_reset_method_attrs,
+	.is_visible = pci_dev_reset_method_attr_is_visible,
+};
+
 /**
  * __pci_reset_function_locked - reset a PCI device function while holding
  * the @dev mutex lock.

drivers/pci/pci.h

@@ -718,4 +718,6 @@ static inline int pci_acpi_program_hp_params(struct pci_dev *dev)
 extern const struct attribute_group aspm_ctrl_attr_group;
 #endif
 
+extern const struct attribute_group pci_dev_reset_method_attr_group;
+
 #endif /* DRIVERS_PCI_H */