Date: Wed, 24 Apr 2024 09:55:29 +0200
From: Pavel Hofman <pavel.hofman@...tera.com>
To: Chris Wulff <Chris.Wulff@...mp.com>,
 "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 James Gruber <jimmyjgruber@...il.com>, Lee Jones <lee@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] usb: gadget: f_uac2: Expose all string descriptors
 through configfs.



On 23. 04. 24 19:22, Chris Wulff wrote:
>> From: Pavel Hofman <pavel.hofman@...tera.com>
>> Sent: Tuesday, April 23, 2024 11:38 AM
> 
>>> +             p_it_name               playback input terminal name
>>> +             p_ot_name               playback output terminal name
>>> +             p_fu_name               playback function unit name
>>> +             p_alt0_name             playback alt mode 0 name
>>> +             p_alt1_name             playback alt mode 1 name
>>
>> Nacked-by: Pavel Hofman <pavel.hofman@...tera.com>
>>
>> I am not sure adding a numbered parameter for every additional alt mode
>> is a way to go for the future. I am not that much concerned about UAC1,
>> but IMO (at least) in UAC2 the configuration method should be flexible
>> for more alt setttings. I can see use cases with many more altsettings.
>>
>> My proposal for adding more alt settings
>> https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/35be4668-58d3-894a-72cf-de1afaacae45@ivitera.com/__;!!HBnMciuwfVSXJQ!TYg7j7-fh3eZAzPfiONi2lo54mf2qsWtpG0nwdaQwSqd1nGdKkTDN8o6_lSIWlWPtHoc-2Nz1KCbRhiXJnzXO8Ku1w$
>> suggested using lists to existing parameters where each item would
>> correspond to the alt setting of the same index (+1). That would allow
>> using more altsettings easily, without having to add parameters to the
>> source code and adding configfs params. I received no feedback. I do not
>> push the param list proposal, but I am convinced an acceptable solution
>> should be discussed thoroughly by the UAC2 gadget stakeholders.
>>
>> I am afraid that once p_alt1_name/c_alt1_name params are accepted, there
>> will be no way back because subsequent removal of configfs params could
>> be viewed as a regression for users.
> 
> I have been thinking about this as well. The alt names are slightly different than the rest of the settings
> since they also include alt mode 0. I was thinking p/c_alt1_name could be expanded to the array so 
> that the entries line up with the other settings and don't have an extra entry for alt 0. Perhaps a different
> name would make more sense.
> 
> Along those lines, I didn't see any gadget drivers using an array of strings for anything, which is also why
> I didn't try to do anything here that merged alt0/1 names into an array. If we were to do an array of strings
> I'm not sure what the best separator would be. Maybe ";"? The rates array uses ",".
> 
> This patch only exposes the existing strings to make them configurable, but I don't want to do anything
> that would preclude a nice interface for extra alt modes.
> 

Thanks a lot for your response. Please can you take a look at
https://lore.kernel.org/linux-usb/72e9b581-4a91-2319-cb9f-0bcb370f34a1@ivitera.com/T/#m68560853b0c7bc2478942d1f953caa2ac95512bd
?

If the params in the upper level were to stand as defaults for the
altsettings (and for the existing altsetting 1 if no specific altset
subdir configs were given), maybe the naming xxx_alt1_xxx could become a
bit confusing. E.g. p_altx_name or p_alt_non0_name?

Thanks a lot,

Pavel.

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