linux-kernel - Re: [PATCH v4 13/36] [media] v4l2: add a frame timeout event

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Date:   Thu, 9 Mar 2017 18:38:18 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Sakari Ailus <sakari.ailus@....fi>, mark.rutland@....com,
        andrew-ct.chen@...iatek.com, minghsiu.tsai@...iatek.com,
        sakari.ailus@...ux.intel.com, nick@...anahar.org,
        songjun.wu@...rochip.com, hverkuil@...all.nl,
        Steve Longerbeam <steve_longerbeam@...tor.com>, pavel@....cz,
        robert.jarzmik@...e.fr, devel@...verdev.osuosl.org,
        markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, shuah@...nel.org,
        geert@...ux-m68k.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, kernel@...gutronix.de, arnd@...db.de,
        mchehab@...nel.org, bparrot@...com, robh+dt@...nel.org,
        horms+renesas@...ge.net.au, tiffany.lin@...iatek.com,
        linux-arm-kernel@...ts.infradead.org,
        niklas.soderlund+renesas@...natech.se, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, jean-christophe.trotin@...com,
        p.zabel@...gutronix.de, fabio.estevam@....com, shawnguo@...nel.org,
        sudipm.mukherjee@...il.com
Subject: Re: [PATCH v4 13/36] [media] v4l2: add a frame timeout event



On 03/05/2017 02:41 PM, Russell King - ARM Linux wrote:
> On Sat, Mar 04, 2017 at 04:37:43PM -0800, Steve Longerbeam wrote:
>>
>>
>> On 03/04/2017 02:56 AM, Sakari Ailus wrote:
>>> That's a bit of a special situation --- still there are alike conditions on
>>> existing hardware. You should return the buffers to the user with the ERROR
>>> flag set --- or return -EIO from VIDIOC_DQBUF, if the condition will
>>> persist:
>>
>> On i.MX an EOF timeout is not recoverable without a stream restart, so
>> I decided to call vb2_queue_error() when the timeout occurs (instead
>> of sending an event). The user will then get -EIO when it attempts to
>> queue or dequeue further buffers.
>
> I'm not sure that statement is entirely accurate.  With the IMX219
> camera, I _could_ (with previous iterations of the iMX capture code)
> stop it streaming, wait a while, and restart it, and everything
> continues to work.

Hi Russell, did you see the "EOF timeout" kernel error message when you
stopped the IMX219 from streaming? Only a "EOF timeout" message
indicates the unrecoverable case.


>
> Are you sure that the problem you have here is caused by the iMX6
> rather than the ADV718x CVBS decoder (your initial description said
> it was the decoder.)

Actually yes I did say it was the adv718x, but in fact I doubt the
adv718x has abruptly stopped data transmission on the bt.656 bus.
I actually suspect the IPU, specifically the CSI. In our experience
the CSI is rather sensitive to glitches and/or truncated frames on the
bt.656 bus and can easily loose vertical sync, and/or lock-up.

Steve

>
> If it _is_ the decoder that's going wrong, that doesn't justify
> cripping the rest of the driver for one instance of broken hardware
> that _might_ be attached to it.
>