Re: [PATCH 2/6] ASoC: SOF: Introduce descriptors for SOF client - Pierre-Louis Bossart

From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"Sridharan, Ranjani" <ranjani.sridharan@intel.com>
Cc: "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
	"tiwai@suse.de" <tiwai@suse.de>,
	"fred.oh@linux.intel.com" <fred.oh@linux.intel.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"parav@nvidia.com" <parav@nvidia.com>,
	"jgg@nvidia.com" <jgg@nvidia.com>,
	"Ertman, David M" <david.m.ertman@intel.com>
Subject: Re: [PATCH 2/6] ASoC: SOF: Introduce descriptors for SOF client
Date: Mon, 5 Oct 2020 10:18:21 -0500	[thread overview]
Message-ID: <074b20bf-ecce-82a9-574a-758da31cef06@linux.intel.com> (raw)
In-Reply-To: <20201005112711.GB401816@kroah.com>

>>>>>>> As you are creating new sysfs directories, you should have
>>>>>>> some
>>>>>>> documentation for them :(
>>>>>> Hi Greg,
>>>>>>
>>>>>> We are not adding any sysfs entries in this series.
>>>>>
>>>>> You added directories in sysfs, right?
>>>> Hi Greg,
>>>>
>>>> We are not adding any sysfs directories.
>>>
>>> Really?  Then what does creating these new devices do in sysfs?  If
>>> nothing, then why are they being used at all?  :)
>>>
>>>> The only change in the /sys directory will be the new ancillary
>>>> devices created in the /sys/bus/ancillary/devices directory ie
>>>> snd_sof_client.ipc_test.0 and snd_sof_client.ipc_test.1.
>>>
>>> That is what I was referring to.
>>>
>>>> In the following patches, we're adding debugfs entries for the ipc
>>>> test clients but no other sysfs changes.
>>>>
>>>> Is it required to add documentation for these as well?
>>>
>>> Why would you not document them?  If you don't do anything with these
>>> devices, then why even use them?  debugfs does not require sysfs
>>> entries, so I fail to see the need for using this api at all here...
>> Hi Greg,
>>
>> Pardon my ignorance here a bit. Typically, when registering platform
>> devices, we've not added any documentation to highlight how they are
>> used. Of course thats no excuse for not doing this right.
>>
>> But just to clarify so that we can fix this properly in the next
>> version, are we expected to add documentation for the directories added
>> in the /sys/bus (ie /sys/bus/ancillary, /sys/bus/ancillary/devices,
>> /sys/bus/ancillary/drivers etc) and also for the devices and drivers
>> added by the SOF driver?
> 
> You are using a brand-new interface, which is designed to represent
> things in the driver model and sysfs properly, and yet your usage
> doesn't actually take advantage of the driver model or sysfs at all?
> 
> That implies to me that you are using this incorrectly.

We are taking advantage of 'standard' sysfs capabilities, e.g. we get a 
power/ directory and can disable pm_runtime if we chose to do so.

But the point is that for now we haven't added domain specific 
properties with attributes.

For example, I noodled with this code last week to replace the platform 
devices with ancillary devices in the Intel SoundWire code, and I get 
this in sysfs:

root@plb:/sys/bus/ancillary/devices/soundwire_intel.link.0# ls -l
total 0
lrwxrwxrwx 1 root root    0 Oct  2 15:48 driver -> 
../../../../bus/ancillary/drivers/intel-sdw
lrwxrwxrwx 1 root root    0 Oct  5 10:12 firmware_node -> 
../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:63/PRP00001:00
drwxr-xr-x 2 root root    0 Oct  5 10:12 power
drwxr-xr-x 5 root root    0 Oct  2 15:48 sdw-master-0
lrwxrwxrwx 1 root root    0 Oct  2 15:48 subsystem -> 
../../../../bus/ancillary
-rw-r--r-- 1 root root 4096 Oct  2 15:48 uevent

What would you want us to document here?