linux-kernel - Re: [PATCH v2 03/10] videobuf2-core: Add helper to get buffer private data from media request

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Message-ID: <20180424083706.cjwhq6nvkmitighq@paasikivi.fi.intel.com>
Date:   Tue, 24 Apr 2018 11:37:06 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>, Pawel Osciak <pawel@...iak.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Alexandre Courbot <acourbot@...omium.org>,
        Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v2 03/10] videobuf2-core: Add helper to get buffer
 private data from media request

Hi Paul,

On Thu, Apr 19, 2018 at 05:41:17PM +0200, Paul Kocialkowski wrote:
> When calling media operation driver callbacks related to media requests,
> only a pointer to the request itself is provided, which is insufficient
> to retrieve the driver's context. Since the driver context is usually
> set as vb2 queue private data and given that the core can determine
> which objects attached to the request are buffers, it is possible to
> extract the associated private data for the first buffer found.
> 
> This is required in order to access the current m2m context from m2m
> drivers' private data in the context of media request operation
> callbacks. More specifically, this allows scheduling m2m device runs
> from the newly-introduced request complete operation.

Rather than fetching a random buffer from the request objects, I'd suggest
to allocate a struct that contains the media request and place the required
information there.

Such as was in my older patchset. The patch won't apply but the approach
would be useful I think.

<URL:https://git.linuxtv.org/sailus/media_tree.git/commit/?h=request&id=f5f6e5925223b445e49279b9fdf070976fd844b9>

> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> ---
>  drivers/media/common/videobuf2/videobuf2-core.c | 15 +++++++++++++++
>  include/media/videobuf2-core.h                  |  1 +
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 13c9d9e243dd..6fa46bfc620f 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -1351,6 +1351,21 @@ bool vb2_core_request_has_buffers(struct media_request *req)
>  }
>  EXPORT_SYMBOL_GPL(vb2_core_request_has_buffers);
>  
> +void *vb2_core_request_find_buffer_priv(struct media_request *req)
> +{
> +	struct media_request_object *obj;
> +	struct vb2_buffer *vb;
> +
> +	obj = media_request_object_find(req, &vb2_core_req_ops, NULL);
> +	if (!obj)
> +		return NULL;
> +
> +	vb = container_of(obj, struct vb2_buffer, req_obj);
> +
> +	return vb2_get_drv_priv(vb->vb2_queue);
> +}
> +EXPORT_SYMBOL_GPL(vb2_core_request_find_buffer_priv);
> +
>  int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb,
>  			 struct media_request *req)
>  {
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 032bd1bec555..65c0cf6afb55 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -1153,4 +1153,5 @@ int vb2_verify_memory_type(struct vb2_queue *q,
>  		enum vb2_memory memory, unsigned int type);
>  
>  bool vb2_core_request_has_buffers(struct media_request *req);
> +void *vb2_core_request_find_buffer_priv(struct media_request *req);
>  #endif /* _MEDIA_VIDEOBUF2_CORE_H */
> -- 
> 2.16.3
> 

-- 
Sakari Ailus
sakari.ailus@...ux.intel.com