linux-kernel - Re: [PATCH] soundwire: debugfs: use controller id instead of link

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Date:   Wed, 3 Feb 2021 16:44:09 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        sanyog.r.kale@...el.com, yung-chuan.liao@...ux.intel.com
Subject: Re: [PATCH] soundwire: debugfs: use controller id instead of link_id

On 02-02-21, 10:43, Pierre-Louis Bossart wrote:
> 
> 
> 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

Key is "The sysfs for properties" is for property files. I am not sure
how this implies for a number above. I was thinking of using ID for N
here and add a link_id file below which represents the link-id property

>  *      |---- 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.

Anyway we are late in cycle for this.. I am reverting this patch and we
can arrive at consensus and fix this for next cycle

Thanks
-- 
~Vinod