[PATCH v5 4/5] cdx: add sysfs for bus reset

[Abhijit Gangurde <abhijit.gangurde@amd.com>]

Add sysfs interface reset to reset all the devices on the CDX bus.

Co-developed-by: Puneet Gupta <puneet.gupta@amd.com>
Signed-off-by: Puneet Gupta <puneet.gupta@amd.com>
Co-developed-by: Nipun Gupta <nipun.gupta@amd.com>
Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Tested-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
---
 Changes in v5:
 - None

 Changes in v4:
 - None

 Changes in v3:
 - None

 Changes in v2:
 - Improve documentation
 - sysfs entry reset takes bus number as an argument

 Documentation/ABI/testing/sysfs-bus-cdx | 15 +++++++++
 drivers/cdx/cdx.c                       | 41 +++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cdx b/Documentation/ABI/testing/sysfs-bus-cdx
index 04c8dfe7e201..d25875359741 100644
--- a/Documentation/ABI/testing/sysfs-bus-cdx
+++ b/Documentation/ABI/testing/sysfs-bus-cdx
@@ -38,6 +38,21 @@ Description:
 
 		  # echo 00 > /sys/bus/cdx/disable
 
+What:		/sys/bus/cdx/reset
+Date:		July 2023
+Contact:	puneet.gupta@amd.com
+Description:
+		Writing bus number in hex to this file will attempt to reset
+		all the devices present on the bus. Resetting a device would
+		clear all existing configuration of the device and put the
+		device in default state. The bus number for the cdx devices can
+		be found at /sys/bus/cdx/devices/cdx-BB:DD, where BB denotes
+		the bus number for the respective device.
+
+		For example ::
+
+		  # echo 00 > /sys/bus/cdx/reset
+
 What:		/sys/bus/cdx/devices/.../vendor
 Date:		March 2023
 Contact:	nipun.gupta@amd.com
diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
index 8da043756fa4..7687b9371210 100644
--- a/drivers/cdx/cdx.c
+++ b/drivers/cdx/cdx.c
@@ -114,6 +114,26 @@ int cdx_dev_reset(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(cdx_dev_reset);
 
+/**
+ * reset_cdx_device - Reset a CDX device
+ * @dev: CDX device
+ * @data: Bus number
+ *    If bus number matches to the device's bus then this device
+ *    is reset else this is no op.
+ *
+ * Return: -errno on failure, 0 on success.
+ */
+static int reset_cdx_device(struct device *dev, void *data)
+{
+	struct cdx_device *cdx_dev = to_cdx_device(dev);
+	u8 bus_num = *((u8 *)data);
+
+	if (cdx_dev->bus_num == bus_num)
+		return cdx_dev_reset(dev);
+
+	return 0;
+}
+
 /**
  * cdx_unregister_device - Unregister a CDX device
  * @dev: CDX device
@@ -520,10 +540,31 @@ static ssize_t rescan_store(const struct bus_type *bus,
 }
 static BUS_ATTR_WO(rescan);
 
+static ssize_t bus_reset_store(const struct bus_type *bus,
+			       const char *buf, size_t count)
+{
+	u8 bus_id;
+	int ret;
+
+	if (kstrtou8(buf, 16, &bus_id))
+		return -EINVAL;
+
+	bus_id = BUS_ID(bus_id);
+	mutex_lock(&cdx_controller_lock);
+	/* Reset all the devices attached to cdx bus */
+	ret = bus_for_each_dev(bus, NULL, (void *)&bus_id, reset_cdx_device);
+	mutex_unlock(&cdx_controller_lock);
+
+	return ret < 0 ? ret : count;
+}
+static struct bus_attribute bus_attr_reset =  __ATTR(reset, 0200, NULL,
+								bus_reset_store);
+
 static struct attribute *cdx_bus_attrs[] = {
 	&bus_attr_enable.attr,
 	&bus_attr_disable.attr,
 	&bus_attr_rescan.attr,
+	&bus_attr_reset.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(cdx_bus);
-- 
2.25.1