[PATCH v7] ufs: core: print UFSHCD capabilities in controller's sysfs node

[Daniil Lunev <dlunev@chromium.org>]

Allows userspace to check if Clock Scaling and Write Booster are
supported.

Signed-off-by: Daniil Lunev <dlunev@chromium.org>

---

Changes in v7:
* Move the comment to the documnetation
* Update the month on the documentation

Changes in v6:
* Add comment to clarify meaning of the "capbilities" sysfs group.

Changes in v5:
* Correct wording for clock scaling.
* Correct wording for the commit message.

Changes in v4:
* Dropped crypto node per Eric Biggers mentioning it can be queried from
  disk's queue node

Changes in v3:
* Expose each capability individually.
* Update documentation to represent new scheme.

Changes in v2:
* Add documentation entry for the new sysfs node.

 Documentation/ABI/testing/sysfs-driver-ufs | 37 ++++++++++++++++++++++
 drivers/ufs/core/ufs-sysfs.c               | 35 ++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-ufs b/Documentation/ABI/testing/sysfs-driver-ufs
index 6b248abb1bd71..78f3e393d2498 100644
--- a/Documentation/ABI/testing/sysfs-driver-ufs
+++ b/Documentation/ABI/testing/sysfs-driver-ufs
@@ -1591,6 +1591,43 @@ Description:	This entry shows the status of HPB.
 
 		The file is read only.
 
+Contact:	Daniil Lunev <dlunev@chromium.org>
+What:		/sys/bus/platform/drivers/ufshcd/*/capabilities/
+What:		/sys/bus/platform/devices/*.ufs/capabilities/
+Date:		August 2022
+Description:	The group represents the effective capabilities of the
+		host-device pair. i.e. the capabilities which are enabled in the
+		driver for the specific host controller, supported by the host
+		controller and are supported and/or have compatible
+		configuration on the device side.
+
+Contact:	Daniil Lunev <dlunev@chromium.org>
+What:		/sys/bus/platform/drivers/ufshcd/*/capabilities/clock_scaling
+What:		/sys/bus/platform/devices/*.ufs/capabilities/clock_scaling
+Date:		August 2022
+Contact:	Daniil Lunev <dlunev@chromium.org>
+Description:	Indicates status of clock scaling.
+
+		== ============================
+		0  Clock scaling is not supported.
+		1  Clock scaling is supported.
+		== ============================
+
+		The file is read only.
+
+What:		/sys/bus/platform/drivers/ufshcd/*/capabilities/write_booster
+What:		/sys/bus/platform/devices/*.ufs/capabilities/write_booster
+Date:		August 2022
+Contact:	Daniil Lunev <dlunev@chromium.org>
+Description:	Indicates status of Write Booster.
+
+		== ============================
+		0  Write Booster can not be enabled.
+		1  Write Booster can be enabled.
+		== ============================
+
+		The file is read only.
+
 What:		/sys/class/scsi_device/*/device/hpb_param_sysfs/activation_thld
 Date:		February 2021
 Contact:	Avri Altman <avri.altman@wdc.com>
diff --git a/drivers/ufs/core/ufs-sysfs.c b/drivers/ufs/core/ufs-sysfs.c
index 0a088b47d5570..75d4287657c80 100644
--- a/drivers/ufs/core/ufs-sysfs.c
+++ b/drivers/ufs/core/ufs-sysfs.c
@@ -279,6 +279,40 @@ static const struct attribute_group ufs_sysfs_default_group = {
 	.attrs = ufs_sysfs_ufshcd_attrs,
 };
 
+static ssize_t clock_scaling_show(struct device *dev, struct device_attribute *attr,
+				  char *buf)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", ufshcd_is_clkscaling_supported(hba));
+}
+
+static ssize_t write_booster_show(struct device *dev, struct device_attribute *attr,
+				  char *buf)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", ufshcd_is_wb_allowed(hba));
+}
+
+static DEVICE_ATTR_RO(clock_scaling);
+static DEVICE_ATTR_RO(write_booster);
+
+/*
+ * See Documentation/ABI/testing/sysfs-driver-ufs for the semantics of this
+ * group.
+ */
+static struct attribute *ufs_sysfs_capabilities_attrs[] = {
+	&dev_attr_clock_scaling.attr,
+	&dev_attr_write_booster.attr,
+	NULL
+};
+
+static const struct attribute_group ufs_sysfs_capabilities_group = {
+	.name = "capabilities",
+	.attrs = ufs_sysfs_capabilities_attrs,
+};
+
 static ssize_t monitor_enable_show(struct device *dev,
 				   struct device_attribute *attr, char *buf)
 {
@@ -1134,6 +1168,7 @@ static const struct attribute_group ufs_sysfs_attributes_group = {
 
 static const struct attribute_group *ufs_sysfs_groups[] = {
 	&ufs_sysfs_default_group,
+	&ufs_sysfs_capabilities_group,
 	&ufs_sysfs_monitor_group,
 	&ufs_sysfs_device_descriptor_group,
 	&ufs_sysfs_interconnect_descriptor_group,
-- 
2.31.0