linux-kernel - Re: [PATCH] media: uvc: limit max bandwidth for HDMI capture

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Message-ID: <20210622102948.47b86fbe@coco.lan>
Date:   Tue, 22 Jun 2021 10:29:48 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        linuxarm@...wei.com, mauro.chehab@...wei.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvc: limit max bandwidth for HDMI capture

Em Mon, 21 Jun 2021 21:22:26 +0300
Laurent Pinchart <laurent.pinchart@...asonboard.com> escreveu:

> Hi Mauro,
> 
> Thank you for the patch.

Thanks for reviewing it!

> 
> On Mon, Feb 01, 2021 at 08:08:59PM +0100, Mauro Carvalho Chehab wrote:
> > This device:
> >         534d:2109 MacroSilicon
> > 
> > Announces that it supports several frame intervals for
> > their resolutions for MJPEG compression:
> > 
> >         VideoStreaming Interface Descriptor:
> >         bLength                            46
> >         bDescriptorType                    36
> >         bDescriptorSubtype                  7 (FRAME_MJPEG)
> >         bFrameIndex                         1
> >         bmCapabilities                   0x00
> >           Still image unsupported
> >         wWidth                           1920
> >         wHeight                          1080
> >         dwMinBitRate                   768000
> >         dwMaxBitRate                196608000
> >         dwMaxVideoFrameBufferSize     4147200
> >         dwDefaultFrameInterval         166666
> >         bFrameIntervalType                  5
> >         dwFrameInterval( 0)            166666
> >         dwFrameInterval( 1)            333333
> >         dwFrameInterval( 2)            400000
> >         dwFrameInterval( 3)            500000
> >         dwFrameInterval( 4)           1000000
> > 
> > However, the highest frame interval (166666), which means 60 fps
> > is not supported. For such resolution, the maximum interval
> > is, instead 333333 (30 fps).  
> 
> What happens if you try to select it ?

Basically, URBs get lost: they cause apps like qv4l2 to crash
sometimes, with:

	v4l-convert: libjpeg error: Corrupt JPEG data: premature end of data segment

The image keeps blinking, and part of the image is replaced by
white noise.

Clearly, it tries to send more data than the maximum available bandwidth
on this chipset.


Sent a v2 addressing the issues you pointed.


Thanks,
Mauro