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

Manivannan Sadhasivam
2020-07-24T05:42:18Z

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@codeaurora.org>
> ---
> 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@codeaurora.org>
> +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.

> +
> +What: /sys/bus/mhi/devices/.../oem_pk_hash
> +Date: July 2020
> +KernelVersion: 5.8
> +Contact: Bhaumik Bhatt <bbhatt@codeaurora.org>
> +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@codeaurora.org>
> L: linux-arm-msm@vger.kernel.org
> 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 '('.

> +{
> + 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,
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);
> --
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> a Linux Foundation Collaborative Project
>