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Subject: Re: [RFC PATCH v2] media: rcar-vin: Allow independent VIN link
 enablement
From:   Steve Longerbeam <slongerbeam@gmail.com>
To:     =?UTF-8?Q?Niklas_S=c3=b6derlund?= <niklas.soderlund@ragnatech.se>
Cc:     linux-media@vger.kernel.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        "open list:MEDIA DRIVERS FOR RENESAS - VIN" 
        <linux-renesas-soc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20190106212018.16519-1-slongerbeam@gmail.com>
 <20190109224039.GD24252@bigcity.dyn.berto.se>
 <da87789d-73e8-663c-a25f-d75e4361ade3@gmail.com>
Message-ID: <8ebc5152-1566-b5f5-1fef-2937b4f2e290@gmail.com>
Date:   Mon, 14 Jan 2019 17:03:35 -0800
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On 1/9/19 5:19 PM, Steve Longerbeam wrote:
>
>
> On 1/9/19 2:40 PM, Niklas Söderlund wrote:
>> Hi Steve,
>>
>> Thanks for your patch, I think it looks good.
>
> Thanks for the Ack! I'm not real familiar with the RFC patch process. 
> Should this be submitted again with RFC stripped from the subject line?

I've been told there isn't really a process for RFC patch submission. I 
will re-submit and strip off the RFC and add your Reviewed-by.

Steve

>
>
>> On 2019-01-06 13:20:18 -0800, Steve Longerbeam wrote:
>>> There is a block of code in rvin_group_link_notify() that loops through
>>> all entities in the media graph, and prevents enabling a link to a VIN
>>> node if any entity is in use. This prevents enabling a VIN link even if
>>> there is an in-use entity somewhere in the graph that is independent of
>>> the link's pipeline.
>>>
>>> For example, the code will prevent enabling a link from the first
>>> rcar-csi2 receiver to a VIN node even if there is an enabled link
>>> somewhere far upstream on the second independent rcar-csi2 receiver
>>> pipeline.
>>>
>>> If this code is meant to prevent modifying a link if any entity in the
>>> graph is actively involved in streaming (because modifying the CHSEL
>>> register fields can disrupt any/all running streams), then the entities
>>> stream counts should be checked rather than the use counts.
>>>
>>> (There is already such a check in __media_entity_setup_link() that 
>>> verifies
>>> the stream_count of the link's source and sink entities are both zero,
>>> but that is insufficient, since there should be no running streams in
>>> the entire graph).
>>>
>>> Modify the media_device_for_each_entity() loop to check the entity
>>> stream_count instead of the use_count, and elaborate on the comment.
>>> VIN node links can now be enabled even if there are other independent
>>> in-use entities that are not streaming.
>>>
>>> Fixes: c0cc5aef31 ("media: rcar-vin: add link notify for Gen3")
>>>
>>> Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
>> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
>>
>>> ---
>>> Changes in v2:
>>> - bring back the media_device_for_each_entity() loop but check the
>>>    stream_count not the use_count.
>>> ---
>>>   drivers/media/platform/rcar-vin/rcar-core.c | 8 ++++++--
>>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/rcar-vin/rcar-core.c 
>>> b/drivers/media/platform/rcar-vin/rcar-core.c
>>> index f0719ce24b97..6dd6b11c1b2b 100644
>>> --- a/drivers/media/platform/rcar-vin/rcar-core.c
>>> +++ b/drivers/media/platform/rcar-vin/rcar-core.c
>>> @@ -131,9 +131,13 @@ static int rvin_group_link_notify(struct 
>>> media_link *link, u32 flags,
>>> !is_media_entity_v4l2_video_device(link->sink->entity))
>>>           return 0;
>>>   -    /* If any entity is in use don't allow link changes. */
>>> +    /*
>>> +     * Don't allow link changes if any entity in the graph is
>>> +     * streaming, because modifying the CHSEL register fields
>>> +     * can disrupt running streams.
>>> +     */
>>>       media_device_for_each_entity(entity, &group->mdev)
>>> -        if (entity->use_count)
>>> +        if (entity->stream_count)
>>>               return -EBUSY;
>>>         mutex_lock(&group->lock);
>>> -- 
>>> 2.17.1
>>>
>