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SubjectRe: [PATCH] soundwire: bus: add enumerated slave to device list
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On 9/9/20 10:54 AM, Srinivas Kandagatla wrote:
>
>
> 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!

It's not necessarily that bad.
- if the intent is to have a single platform firmware that can deal with
different boards, it's a good thing.
- but if it's just sloppy platform firmware that just does copy-paste
from platform to platform then indeed it becomes a mess.

> May be we could make the enumerated devices discovery bit more verbose!

Maybe adding a device number sysfs entry would help, e.g. reporting
NotAttched or a value in [0,11] would tell you if the device is actually
present.


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