[PATCH v2] ufs: core: print capabilities in controller's sysfs node

[PATCH v2] ufs: core: print capabilities in controller's sysfs node

[Daniil Lunev]

Allows userspace to check supported by the controller/device
functionality, e.g. write booster.

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

---

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

 Documentation/ABI/testing/sysfs-driver-ufs |  9 +++++++++
 drivers/ufs/core/ufs-sysfs.c               | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-ufs b/Documentation/ABI/testing/sysfs-driver-ufs
index 6b248abb1bd71..97e42e4763eaf 100644
--- a/Documentation/ABI/testing/sysfs-driver-ufs
+++ b/Documentation/ABI/testing/sysfs-driver-ufs
@@ -1591,6 +1591,15 @@ Description:	This entry shows the status of HPB.
 
 		The file is read only.
 
+What:		/sys/bus/platform/drivers/ufshcd/*/caps
+What:		/sys/bus/platform/devices/*.ufs/caps
+Date:		July 2022
+Contact:	Daniil Lunev <dlunev@chromium.org>
+Description:	Read-only attribute. Enabled capabilities of the UFS driver. The
+		enabled capabilities are determined by what is supported by the
+		host controller and the UFS device.
+		Format: 0x%08llx
+
 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..b0c294c367519 100644
--- a/drivers/ufs/core/ufs-sysfs.c
+++ b/drivers/ufs/core/ufs-sysfs.c
@@ -254,6 +254,14 @@ static ssize_t wb_on_store(struct device *dev, struct device_attribute *attr,
 	return res < 0 ? res : count;
 }
 
+static ssize_t caps_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct ufs_hba *hba = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "0x%08llx\n", hba->caps);
+}
+
 static DEVICE_ATTR_RW(rpm_lvl);
 static DEVICE_ATTR_RO(rpm_target_dev_state);
 static DEVICE_ATTR_RO(rpm_target_link_state);
@@ -262,6 +270,7 @@ static DEVICE_ATTR_RO(spm_target_dev_state);
 static DEVICE_ATTR_RO(spm_target_link_state);
 static DEVICE_ATTR_RW(auto_hibern8);
 static DEVICE_ATTR_RW(wb_on);
+static DEVICE_ATTR_RO(caps);
 
 static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
 	&dev_attr_rpm_lvl.attr,
@@ -272,6 +281,7 @@ static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
 	&dev_attr_spm_target_link_state.attr,
 	&dev_attr_auto_hibern8.attr,
 	&dev_attr_wb_on.attr,
+	&dev_attr_caps.attr,
 	NULL
 };
 
-- 
2.31.0

Re: [PATCH v2] ufs: core: print capabilities in controller's sysfs node

[Bart Van Assche]

On 7/28/22 16:05, Daniil Lunev wrote:
> +What:		/sys/bus/platform/drivers/ufshcd/*/caps
> +What:		/sys/bus/platform/devices/*.ufs/caps
> +Date:		July 2022
> +Contact:	Daniil Lunev <dlunev@chromium.org>
> +Description:	Read-only attribute. Enabled capabilities of the UFS driver. The
> +		enabled capabilities are determined by what is supported by the
> +		host controller and the UFS device.
> +		Format: 0x%08llx

This documentation is useless since the meaning of the individual bits 
has not been documented.

Thanks,

Bart.

Re: [PATCH v2] ufs: core: print capabilities in controller's sysfs node

[Greg Kroah-Hartman]

On Thu, Jul 28, 2022 at 04:23:16PM -0700, Bart Van Assche wrote:
> On 7/28/22 16:05, Daniil Lunev wrote:
> > +What:		/sys/bus/platform/drivers/ufshcd/*/caps
> > +What:		/sys/bus/platform/devices/*.ufs/caps
> > +Date:		July 2022
> > +Contact:	Daniil Lunev <dlunev@chromium.org>
> > +Description:	Read-only attribute. Enabled capabilities of the UFS driver. The
> > +		enabled capabilities are determined by what is supported by the
> > +		host controller and the UFS device.
> > +		Format: 0x%08llx
> 
> This documentation is useless since the meaning of the individual bits has
> not been documented.

Yeah, that's not ok, where are these bits coming from and what userspace
tools will be using them?

thanks,

greg k-h

Re: [PATCH v2] ufs: core: print capabilities in controller's sysfs node

[Daniil Lunev]

> Yeah, that's not ok, where are these bits coming from
There has been a few more iterations on the patch, in the latest state only
Clock Scaling and Write Booster are exposed as individual nodes.

> what userspace tools will be using them?
In ChromeOS we want to explicitly control WriteBooster state, but for that
the user space needs to know when it is supported but off, and when it is
not supported at all. On top of it, Clock Scaling complicates the story since
it disables the control via wb_on node. That is something I need to figure
out separately.

--Daniil