linux-kernel - Re: [PATCH] soundwire: bus: add enumerated slave to device list

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Date:   Wed, 9 Sep 2020 16:54:22 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        vkoul@...nel.org, yung-chuan.liao@...ux.intel.com
Cc:     sanyog.r.kale@...el.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soundwire: bus: add enumerated slave to device list



On 09/09/2020 15:39, Pierre-Louis Bossart wrote:
> 
>>>> Currently slave devices are only added either from device tree or acpi
>>>> entries. However lets say, there is wrong or no entry of a slave device
>>>> in DT that is enumerated, then there is no way for user to know all
>>>> the enumerated devices on the bus.
>>>
>>> Sorry Srinivas, I don't understand your point.
>>>
>>> The sysfs entries will include all devices that are described in 
>>> platform firmware (be it DT or ACPI).
>>
>> yes that is true, but it will not include all the enumerated devices 
>> on the bus!
>>
>> In my case on a new board I was trying to figure out what devices are 
>> on the bus even before even adding any device tree entries!
> 
> We've seen this before but dynamic debug provides all the information 
> you need. see e.g. the logs from 
> https://sof-ci.01.org/linuxpr/PR2425/build4447/devicetest/
> 
> jf-cml-rvp-sdw-1 kernel: [  289.751974] soundwire sdw-master-0: Slave 
> attached, programming device number
> jf-cml-rvp-sdw-1 kernel: [  289.752121] soundwire sdw-master-0: SDW 
> Slave Addr: 10025d070000 <<< HERE

Yes, I have noticed this too! This will be printed for every call to 
sdw_extract_slave_id()!

...
> 
> Now I get your point but
> a) you already have a dynamic debug trace to list all devices
> b) adding 'undeclared' devices would make things quite murky and is only 
> half of the solution. We already struggle because we already have 
> 'ghost' devices in sysfs that are not physically present, and no way to 
> differentiate between the two. If we did add those entries, then we'd 
> need two new sysfs attributes such as
> 'declared' and 'enumerated'.

I totally agree with you on dealing with the undeclared devices, which 
is unnecessary mess!
May be we could make the enumerated devices discovery bit more verbose!

--srini