linux-kernel - Re: [PATCH 1/2] usb: gadget: f_uac2: Stop endpoint before enabling it.

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Date:   Sun, 25 Apr 2021 11:28:52 +0800
From:   Peter Chen <peter.chen@...nel.org>
To:     Pawel Laszczak <pawell@...ence.com>
Cc:     "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "ruslan.bilovol@...il.com" <ruslan.bilovol@...il.com>,
        "jbrunet@...libre.com" <jbrunet@...libre.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rahul Kumar <kurahul@...ence.com>
Subject: Re: [PATCH 1/2] usb: gadget: f_uac2: Stop endpoint before enabling
 it.

On 21-04-23 18:49:14, Peter Chen wrote:
> On 21-04-20 03:56:25, Pawel Laszczak wrote:
> > >On 21-04-19 09:50:53, Pawel Laszczak wrote:
> > >> From: Pawel Laszczak <pawell@...ence.com>
> > >>
> > >> Patch adds disabling endpoint before enabling it during changing
> > >> alternate setting. Lack of this functionality causes that in some
> > >> cases uac2 queue the same request multiple time.
> > >> Such situation can occur when host send set interface with
> > >> alternate setting 1 twice.
> > >>
> > >> Signed-off-by: Pawel Laszczak <pawell@...ence.com>
> > >> ---
> > >>  drivers/usb/gadget/function/f_uac2.c | 8 ++++----
> > >>  1 file changed, 4 insertions(+), 4 deletions(-)
> > >>
> > >> diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
> > >> index 9cc5c512a5cd..7d20a9d8a1b4 100644
> > >> --- a/drivers/usb/gadget/function/f_uac2.c
> > >> +++ b/drivers/usb/gadget/function/f_uac2.c
> > >> @@ -890,17 +890,17 @@ afunc_set_alt(struct usb_function *fn, unsigned intf, unsigned alt)
> > >>  	if (intf == uac2->as_out_intf) {
> > >>  		uac2->as_out_alt = alt;
> > >>
> > >> +		u_audio_stop_capture(&uac2->g_audio);
> > >> +
> > >>  		if (alt)
> > >>  			ret = u_audio_start_capture(&uac2->g_audio);
> > >> -		else
> > >> -			u_audio_stop_capture(&uac2->g_audio);
> > >>  	} else if (intf == uac2->as_in_intf) {
> > >>  		uac2->as_in_alt = alt;
> > >>
> > >> +		u_audio_stop_playback(&uac2->g_audio);
> > >> +
> > >>  		if (alt)
> > >>  			ret = u_audio_start_playback(&uac2->g_audio);
> > >> -		else
> > >> -			u_audio_stop_playback(&uac2->g_audio);
> > >>  	} else {
> > >>  		dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
> > >>  		return -EINVAL;
> > >
> > >To avoid this, you may use prm->ep_enabled to judge if the endpoint has
> > >already enabled.
> > 
> > Such condition is as first instruction inside u_audio_stop_playback->free_ep  function,
> > so we don't need duplicate it here.
> > 
> 
> Get your points, you may add more explanations both the code your change
> and the commit log.
> 

After thinking more, I think it is better add judge code at
u_audio_start_playback/capture, but not change code here. The reader may
not understand the code your change at the first glance.

-- 

Thanks,
Peter Chen