Re: [PATCH] soundwire: debugfs: use controller id instead of link_id

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 2/1/21 10:18 PM, Vinod Koul wrote:
> On 01-02-21, 10:10, Pierre-Louis Bossart wrote:
>> On 2/1/21 4:14 AM, Vinod Koul wrote:
>>> On 21-01-21, 17:23, Srinivas Kandagatla wrote:
>>>> On 21/01/2021 15:12, Pierre-Louis Bossart wrote:
>>>>> On 1/21/21 6:03 AM, Srinivas Kandagatla wrote:
> 
>>>> I totally agree!
>>>>
>>>> If I understand it correctly in Intel case there will be only one Link ID
>>>> per bus.
>>>
>>> Yes IIUC there would be one link id per bus.
>>>
>>> the ida approach gives us unique id for each master,bus I would like to
>>> propose using that everywhere
>>
>> We have cases where link2 is not used but link0, 1 and 3 are.
>> Using the IDA would result in master-0,1,2 being shown, that would throw the
>> integrator off. the link_id is related to hardware and can tolerate gaps,
>> the IDA is typically always increasing and is across the system, not
>> controller specific.
>>
>> We can debate forever but both pieces of information are useful, so my
>> recommendation is to use both:
>>
>> snprintf(name, sizeof(name), "master-%d-%d", bus_id, bus->link_id);
> 
> I agree we should use both, but does it really make sense for naming? We
> can keep name in ida and expose the link_id as a parameter for
> integrators to see in sysfs.

That would mean changing the meaning of sysfs properties:

/*
  * The sysfs for properties reflects the MIPI description as given
  * in the MIPI DisCo spec
  *
  * Base file is:
  *	sdw-master-N
  *      |---- revision
  *      |---- clk_stop_modes
  *      |---- max_clk_freq
  *      |---- clk_freq
  *      |---- clk_gears
  *      |---- default_row
  *      |---- default_col
  *      |---- dynamic_shape
  *      |---- err_threshold
  */

N is the link ID in the spec. I am not convinced we'd do the community a 
service by unilaterally changing what an external spec means, or add a 
property that's kernel-defined while the rest is supposed to come from 
firmware. If you want to change the spec then you can contribute 
feedback in MIPI circles (MIPI have a mechanism for maintainers to 
provide such feedback without company/employer membership requirements)

So either we add a sysfs layer that represents a controller (better in 
my opinion so that we can show the link/master count), or keep the 
existing hierarchy but expand the name with a unique ID so that Qualcomm 
don't get errors with duplicate sysfs link0 entries.