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

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Message-ID: <562F41A3.3070504@felipetonello.com>
Date:	Tue, 27 Oct 2015 09:19:31 +0000
From:	Felipe Ferreri Tonello <eu@...ipetonello.com>
To:	Robert Baldyga <r.baldyga@...sung.com>,
	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 27/10/15 06:47, Robert Baldyga wrote:
> On 10/26/2015 11:53 PM, Felipe Tonello wrote:
>> 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?
> 
> They are copied for each instance of USB function, so they are actually
> template to fill and copy in bind(). I'm currently working on some
> patches changing a bit behavior of set_alt() to make it clearer, but for
> now the only way to distinguish between altsettings properly is to store
> bInterfaceNumber value for each function instance in its bind().

Ok. Thanks.

-- 
Felipe
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