linux-kernel - Re: [PATCH 2/5] media: v4l2-core changes to use media tuner token api

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Message-ID: <54208A03.2010101@osg.samsung.com>
Date:	Mon, 22 Sep 2014 14:43:47 -0600
From:	Shuah Khan <shuahkh@....samsung.com>
To:	Devin Heitmueller <dheitmueller@...nellabs.com>
CC:	Hans Verkuil <hverkuil@...all.nl>, Antti Palosaari <crope@....fi>,
	m.chehab@...sung.com, laurent.pinchart@...asonboard.com,
	gregkh@...uxfoundation.org, sakari.ailus@...ux.intel.com,
	ramakrmu@...co.com, dheitmueller@...nellabs.co, olebowle@....com,
	akpm@...ux-foundation.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 2/5] media: v4l2-core changes to use media tuner token
 api

Hi Devin,

On 09/22/2014 01:21 PM, Devin Heitmueller wrote:
> Hi Shuah,
> 
> What about G_INPUT and G_TUNER?  Consider the following use case, which is
> entirely legal in the V4L2 API:

Did you mean G_INPUT and G_STD here? I didn't see G_TUNER mentioned
below in the use-case.

I didn't know this use-case, I did notice ENUM_INPUT getting called
in a loop during testing. I think I didn't run into this because I
changed the au0828: vidioc_g_tuner to hold the lock as it does a tuner
init and messes up the tuner when it is in use by dvb. But, that doesn't
cover this use-case for other drivers. So I need to make more changes
to cover it. Thanks for pointing this out.

> 
> 1.  Program opens /dev/video0
> 2.  Program calls G_INPUT/G_STD and sees that the appropriate input and
> standard are already set, since all devices have a default input at
> initialization
> 3.  Program never calls S_INPUT, S_STD, or S_TUNER
> 4.  Program goes into a loop calling ENUM_INPUT, waiting until it returns
> the input as having signal lock
> 5.  When signal lock is seen, program calls STREAMON.

I am missing vb2 streamon change to hold the tuner in this patch set.
Without that change vb2 work isn't complete. Unfortunately I don't
have hybrid hardware that uses a vb2 driver.

> 
> In the above case, you would be actively using the au8522 video decoder but
> not holding the lock, so thr DVB device can be opened and screw everything
> up.  Likewise if the DVB device were in use and such a program were run, it
> wouls break.
> 

I think this use-case will be covered with changes to vb2 streamon
to check and hold tuner. I am thinking it might not be necessary to
change g_tuner, g_std, g_input and enum_input at v4l2-core level.
Does that sounds right??

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shuahkh@....samsung.com | (970) 217-8978
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