Re: [PATCH 3/5] usb: gadget: gmidi: remove bus powered requirement on bmAttributes

From: Krzysztof Opasiak
Date: Tue Mar 08 2016 - 05:15:10 EST

On 03/08/2016 08:43 AM, Felipe Balbi wrote:

>>>> This is necessary because this driver is actually wrong in which is
>>>> asking for the host to power itself. This is not specified on USB-MIDI
>>>> specification, neither makes any sense since this configuration is
>>>> device specific.
>>>> What is your suggestion to make it configurable? Maybe at compile-time?
>>>> I really don't know what is the best solution if this is not something
>>>> you like it.
>>> well, you could use our configfs-based gadget interface. You don't
>>> really need to use gmidi.ko at all. In fact, we wanna do away with any
>>> static modules and rely only on configfs. If configfs doesn't let you
>>> change what you want/need, then we can talk about adding support for
>>> those.
>>> bMaxPower and bmAttributes sound like good things to have configurable
>>> over configfs but beware of what the USB specification says about them,
>>> we cannot let users violate the spec by passing bogus values on these
>>> fields.
>> I agree that we should move to configfs, but the truth is that these
>> legacy devices are still useful. They just do one thing, mostly, but
> yes, they are useful as they are. They don't need to be changed to be
> useful. Plus, you can have a gadget built with configfs that does only
> one thing. And you can do that with a simple shell script.
>> its easy and simple to setup and use. So I think before we have some
> so is configfs.
>> sort of preset library of configfs-based gadget drivers, we still need
>> these modules.
> there is already a library called libusbg.

As libusbg itself is a little bit dead there is a fork called
libusbgx[1] and it is still active;)

It already has support for f_midi so it is ready to use.

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Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics