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

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Date:	Mon, 26 Oct 2015 23:30:01 +0100
From:	Robert Baldyga <r.baldyga@...kerion.com>
To:	"Felipe F. Tonello" <eu@...ipetonello.com>,
	linux-usb@...r.kernel.org
Cc:	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

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().

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

Best regards,
Robert

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