linux-kernel - Re: [RFC PATCH v2] media: rcar-vin: Allow independent VIN link enablement

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Date:   Wed, 9 Jan 2019 17:19:37 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Niklas Söderlund <niklas.soderlund@...natech.se>
Cc:     linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "open list:MEDIA DRIVERS FOR RENESAS - VIN" 
        <linux-renesas-soc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2] media: rcar-vin: Allow independent VIN link
 enablement



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?

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@...il.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.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
>>