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

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Date:   Tue, 19 Jan 2021 09:54:17 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     alsa-devel@...a-project.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.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 1/19/21 8:52 AM, Vinod Koul wrote:
> On 15-01-21, 16:25, Srinivas Kandagatla wrote:
>> link_id can be zero and if we have multiple controller instances
>> in a system like Qualcomm debugfs will end-up with duplicate namespace
>> resulting in incorrect debugfs entries.
>>
>> Using id should give a unique debugfs directory entry and should fix below
>> warning too.
>> "debugfs: Directory 'master-0' with parent 'soundwire' already present!"
> 
> Yeah id is guaranteed to be unique so this will work.
> 
> Applied, thanks

This patch is a no-op for Intel, but I am not convinced it's the right 
fix or the definitions are not consistent.

  * @link_id: Link id number, can be 0 to N, unique for each Master
  * @id: bus system-wide unique id

In the MIPI/DisCo definitions, a controller can have multiple masters. 
if you have multiple controllers, each of them should have their own 
debugfs directory IMHO. It's totally fine to have multiple bus/masters 
with a link_id == 0.