Re: [PATCH v5 10/10] bus: mhi: core: Introduce sysfs entries for MHI

From: bbhatt
Date: Mon Jul 27 2020 - 20:29:50 EST

On 2020-07-23 22:42, Manivannan Sadhasivam wrote:
On Thu, Jul 23, 2020 at 03:36:42PM -0700, Bhaumik Bhatt wrote:
Introduce sysfs entries to enable userspace clients the ability to read
the serial number and the OEM PK Hash values obtained from BHI. OEMs
need to read these device-specific hardware information values through
userspace for factory testing purposes and cannot be exposed via degbufs
as it may remain disabled for performance reasons. Also, update the
documentation for ABI to include these entries.

Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
---
Documentation/ABI/stable/sysfs-bus-mhi | 25 ++++++++++++++++
MAINTAINERS | 1 +
drivers/bus/mhi/core/init.c | 53 ++++++++++++++++++++++++++++++++++
3 files changed, 79 insertions(+)
create mode 100644 Documentation/ABI/stable/sysfs-bus-mhi

diff --git a/Documentation/ABI/stable/sysfs-bus-mhi b/Documentation/ABI/stable/sysfs-bus-mhi
new file mode 100644
index 0000000..a4e4bd2
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-bus-mhi
@@ -0,0 +1,25 @@
+What: /sys/bus/mhi/devices/.../serialnumber
+Date: July 2020
+KernelVersion: 5.8
+Contact: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
+Description:
+ The file holds the serial number of the client device obtained
+ using a BHI (Boot Host Interface) register read after at least
+ one attempt to power up the device has been done. If read
+ without having the device power on at least once, the file will
+ read all 0's.
+Users: Any userspace application or clients interested in the device
+ hardware information.

Please align all the fields onto a single starting point. Have a look at other
ABI documentation like, Documentation/ABI/stable/sysfs-bus-vmbus.

Alignment was updated. Seems OK to me actually, I am unsure why the patch shows up as
slightly different on email.
+
+What: /sys/bus/mhi/devices/.../oem_pk_hash
+Date: July 2020
+KernelVersion: 5.8
+Contact: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
+Description:
+ The file holds the OEM PK Hash value of the endpoint device
+ obtained using a BHI (Boot Host Interface) register read after
+ at least one attempt to power up the device has been done. If
+ read without having the device power on at least once, the file
+ will read all 0's.
+Users: Any userspace application or clients interested in the device
+ hardware information.
diff --git a/MAINTAINERS b/MAINTAINERS
index e64e5db..5e49316 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11018,6 +11018,7 @@ M: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
L: linux-arm-msm@xxxxxxxxxxxxxxx
S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/mani/mhi.git
+F: Documentation/ABI/stable/sysfs-bus-mhi
F: Documentation/mhi/
F: drivers/bus/mhi/
F: include/linux/mhi.h
diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
index d2c0f6e..a7b0d76 100644
--- a/drivers/bus/mhi/core/init.c
+++ b/drivers/bus/mhi/core/init.c
@@ -76,6 +76,56 @@ const char *to_mhi_pm_state_str(enum mhi_pm_state state)
return mhi_pm_state_str[index];
}

+static ssize_t serial_number_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)

We haven't followed this before but it is good to align the function parameters
with respect to '('.

This one too, I have made sure it is aligned with the '('. Maybe a re-upload should
clear it up.
+{
+ struct mhi_device *mhi_dev = to_mhi_device(dev);
+ struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
+
+ return snprintf(buf, PAGE_SIZE, "Serial Number: %u\n",
+ mhi_cntrl->serial_number);

We need to think about what happens if the mhi_cntrl structure is not zero
initialized by the controller driver. All throughout the stack we assume that
the mhi_cntrl struct is zero initialized but things can go awry if it was not
the case!

There was one API in the downstream (mhi_alloc_controller()) for this purpose
but I removed it since we ended up with just a kzalloc(). Does it make sense to
introduce it now?

Thanks for pointing out. I realize this could have potential consequences and have added
the patch to introduce the API as a dependency.
Thanks,
Mani

+}
+static DEVICE_ATTR_RO(serial_number);
+
+static ssize_t oem_pk_hash_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct mhi_device *mhi_dev = to_mhi_device(dev);
+ struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
+ int i, cnt = 0;
+
+ for (i = 0; i < ARRAY_SIZE(mhi_cntrl->oem_pk_hash); i++)
+ cnt += snprintf(buf + cnt, PAGE_SIZE - cnt,
+ "OEMPKHASH[%d]: 0x%x\n", i,
+ mhi_cntrl->oem_pk_hash[i]);
+
+ return cnt;
+}
+static DEVICE_ATTR_RO(oem_pk_hash);
+
+static struct attribute *mhi_sysfs_attrs[] = {
+ &dev_attr_serial_number.attr,
+ &dev_attr_oem_pk_hash.attr,
+ NULL,
+};
+
+static const struct attribute_group mhi_sysfs_group = {
+ .attrs = mhi_sysfs_attrs,
+};
+
+static int mhi_create_sysfs(struct mhi_controller *mhi_cntrl)
+{
+ return sysfs_create_group(&mhi_cntrl->mhi_dev->dev.kobj,
+ &mhi_sysfs_group);
+}
+
+static void mhi_destroy_sysfs(struct mhi_controller *mhi_cntrl)
+{
+ sysfs_remove_group(&mhi_cntrl->mhi_dev->dev.kobj, &mhi_sysfs_group);
+}
+
/* MHI protocol requires the transfer ring to be aligned with ring length */
static int mhi_alloc_aligned_ring(struct mhi_controller *mhi_cntrl,
struct mhi_ring *ring,
@@ -917,6 +967,8 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
mhi_cntrl->mhi_dev = mhi_dev;

mhi_create_debugfs(mhi_cntrl);
+ if (mhi_create_sysfs(mhi_cntrl))
+ dev_err(mhi_cntrl->cntrl_dev, "Failed to create sysfs entries\n");

return 0;

@@ -940,6 +992,7 @@ void mhi_unregister_controller(struct mhi_controller *mhi_cntrl)
struct mhi_chan *mhi_chan = mhi_cntrl->mhi_chan;
unsigned int i;

+ mhi_destroy_sysfs(mhi_cntrl);
mhi_destroy_debugfs(mhi_cntrl);

kfree(mhi_cntrl->mhi_cmd);
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project