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

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Date:   Wed, 9 Jan 2019 23:40:39 +0100
From:   Niklas Söderlund 
        <niklas.soderlund@...natech.se>
To:     Steve Longerbeam <slongerbeam@...il.com>
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

Hi Steve,

Thanks for your patch, I think it looks good.

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
> 

-- 
Regards,
Niklas Söderlund