linux-kernel - Re: [PATCH v4 5/7] usb: gadget: f_midi: set altsettings only for MIDIStreaming interface

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Message-ID: <CAGrhNMz9aRERVKOVn82WP7R1pZ9wAVV=DnCee87FjfEo1-v3-Q@mail.gmail.com>
Date:	Mon, 26 Oct 2015 22:53:34 +0000
From:	Felipe Tonello <eu@...ipetonello.com>
To:	Robert Baldyga <r.baldyga@...kerion.com>
Cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	Clemens Ladisch <clemens@...isch.de>
Subject: Re: [PATCH v4 5/7] usb: gadget: f_midi: set altsettings only for
 MIDIStreaming interface

Hi Robert,

On Mon, Oct 26, 2015 at 10:30 PM, Robert Baldyga
<r.baldyga@...kerion.com> wrote:
> On 10/26/2015 05:55 PM, Felipe F. Tonello wrote:
>> This avoids duplication of USB requests for OUT endpoint and
>> re-enabling endpoints.
>>
>> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>> ---
>>  drivers/usb/gadget/function/f_midi.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>> index 0e9cdeb..a617df3 100644
>> --- a/drivers/usb/gadget/function/f_midi.c
>> +++ b/drivers/usb/gadget/function/f_midi.c
>> @@ -323,6 +323,10 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>       unsigned i;
>>       int err;
>>
>> +     /* We don't care if it is not MIDIStreaming interface */
>> +     if (intf != ms_interface_desc.bInterfaceNumber)
>> +             return 0;
>> +
>
> These global descriptors are overwritten in bind() of each instance of
> f_midi, so you have no guarantee that your bInterfaceNumber is correct
> for your current instance. Instead you should store value obtained from
> usb_interface_id() during bind().

Ok.

But then this interface descriptors shouldn't be global static,
because they will always reflect the latest bind() only. Right?

>
>>       err = f_midi_start_ep(midi, f, midi->in_ep);
>>       if (err)
>>               return err;
>>

Felipe
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