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

[bbhatt@codeaurora.org]

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@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.
> 
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@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 '('.
> 
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
>>