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Date: Wed, 14 Aug 2024 16:10:53 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Xu Yang <xu.yang_2@nxp.com>
Cc: laurent.pinchart@ideasonboard.com, dan.scally@ideasonboard.com,
	m.grzeschik@pengutronix.de, jun.li@nxp.com, imx@lists.linux.dev,
	linux-usb@vger.kernel.org
Subject: Re: [RESEND] usb: gadget: uvc: queue pump work in uvcg_video_enable()
Message-ID: <2024081438-power-surplus-d4d4@gregkh>
References: <20240814112537.2608949-1-xu.yang_2@nxp.com>
 <2024081405-sample-duckbill-ffec@gregkh>
 <20240814134802.tksdhu7yexuuknqy@hippo>
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In-Reply-To: <20240814134802.tksdhu7yexuuknqy@hippo>

On Wed, Aug 14, 2024 at 09:48:02PM +0800, Xu Yang wrote:
> On Wed, Aug 14, 2024 at 01:47:23PM +0200, Greg KH wrote:
> > On Wed, Aug 14, 2024 at 07:25:37PM +0800, Xu Yang wrote:
> > > Since commit "6acba0345b68 usb:gadget:uvc Do not use worker thread to pump
> > > isoc usb requests", pump work could only be queued in uvc_video_complete()
> > > and uvc_v4l2_qbuf(). If VIDIOC_QBUF is executed before VIDIOC_STREAMON,
> > > we can only depend on uvc_video_complete() to queue pump work. However,
> > > this requires some free requests in req_ready list. If req_ready list is
> > > empty all the time, pump work will never be queued and video datas will
> > > never be pumped to usb controller. Actually, this situation could happen
> > > when run uvc-gadget with static image:
> > > 
> > > $ ./uvc-gadget -i 1080p.jpg uvc.0
> > > 
> > > When capture image from this device, the user app will always block there.
> > > 
> > > The issue is uvc driver has queued video buffer before streamon, but the
> > > req_ready list is empty all the time after streamon. This will queue pump
> > > work in uvcg_video_enable() to fill some request to req_ready list so the
> > > uvc device could work properly.
> > > 
> > > Fixes: 6acba0345b68 ("usb:gadget:uvc Do not use worker thread to pump isoc usb requests")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> > > ---
> > >  drivers/usb/gadget/function/uvc_video.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > 
> > Why is this a RESEND?  What happened to the first one to require this?
> 
> I accidentally forgot to cc usb maillist in previous one. So I resend it.

Please always tell us why you are doing something, otherwise we have no
idea :(