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Date: Thu, 22 Jan 2015 08:05:18 -0700
From: Shuah Khan <shuahkh@osg.samsung.com>
Organization: Samsung Open Source Group
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To: Devin Heitmueller <dheitmueller@kernellabs.com>,
        "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
CC: Mauro Carvalho Chehab <m.chehab@samsung.com>,
        Hans Verkuil <hans.verkuil@cisco.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        laurent pinchart <laurent.pinchart@ideasonboard.com>,
        ttmesterr <ttmesterr@gmail.com>,
        linux-media <linux-media@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/3] media: au0828 - convert to use videobuf2
References: <cover.1421115389.git.shuahkh@osg.samsung.com> <9642c73eb38234cd69059c4a64bfde5205d637c2.1421115389.git.shuahkh@osg.samsung.com> <CA+V-a8uzfcyhO0vA2Jxg8YJYrHtk_b0skhN4kGCwO81X9yF--w@mail.gmail.com> <CAGoCfiw4Sehjk0_7KWo3tQZabn1w8nVM+8WTgY2sSkL0FSZWOQ@mail.gmail.com>
In-Reply-To: <CAGoCfiw4Sehjk0_7KWo3tQZabn1w8nVM+8WTgY2sSkL0FSZWOQ@mail.gmail.com>
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On 01/22/2015 08:00 AM, Devin Heitmueller wrote:
>>> -       fh->type = type;
>>> -       fh->dev = dev;
>>> -       v4l2_fh_init(&fh->fh, vdev);
>>> -       filp->private_data = fh;
>>> +       dprintk(1,
>>> +               "%s called std_set %d dev_state %d stream users %d users %d\n",
>>> +               __func__, dev->std_set_in_tuner_core, dev->dev_state,
>>> +               dev->streaming_users, dev->users);
>>>
>>> -       if (mutex_lock_interruptible(&dev->lock)) {
>>> -               kfree(fh);
>>> +       if (mutex_lock_interruptible(&dev->lock))
>>>                 return -ERESTARTSYS;
>>> +
>>> +       ret = v4l2_fh_open(filp);
>>> +       if (ret) {
>>> +               au0828_isocdbg("%s: v4l2_fh_open() returned error %d\n",
>>> +                               __func__, ret);
>>> +               mutex_unlock(&dev->lock);
>>> +               return ret;
>>>         }
>>> +
>>>         if (dev->users == 0) {
>>
>> you can use v4l2_fh_is_singular_file() and get rid of users member ?
> 
> That won't work because the underlying resources are shared between
> /dev/videoX and /dev/vbiX device nodes.  Hence if you were to move to
> v4l2_fh_is_singular_file(), the video device would get opened, the
> stream would get reset, the VBI device would get opened, and that
> would cause the analog stream to get enabled/reset *again*.
> 

Thanks Devin for a detailed explanation. I did see this behavior when I
was removed users and used v4l2_fh_is_singular_file() instead. I didn't
understand that this is due to resource sharing between /dev/videoX and
/dev/vbiX .

thanks,
-- Shuah


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