linux-kernel - Re: [PATCH 02/20] drm: Remove users of drm_format_(horz|vert)_chroma

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Date:   Wed, 17 Apr 2019 15:32:17 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org,
        Emil Velikov <emil.velikov@...labora.com>
Subject: Re: [PATCH 02/20] drm: Remove users of
 drm_format_(horz|vert)_chroma_subsampling

On Wed, 2019-04-17 at 09:54 +0200, Maxime Ripard wrote:
> drm_format_horz_chroma_subsampling and drm_format_vert_chroma_subsampling
> are basically a lookup in the drm_format_info table plus an access to the
> hsub and vsub fields of the appropriate entry.
> 
> Most drivers are using this function while having access to the entry
> already, which means that we will perform an unnecessary lookup. Removing
> the call to these functions is therefore more efficient.
> 
> Some drivers will not have access to that entry in the function, but in
> this case the overhead is minimal (we just have to call drm_format_info()
> to perform the lookup) and we can even avoid multiple, inefficient lookups
> in some places that need multiple fields from the drm_format_info
> structure.
> 
> This is amplified by the fact that most of the time the callers will have
> to retrieve both the vsub and hsub fields, meaning that they would perform
> twice the lookup.
> 
> Reviewed-by: Emil Velikov <emil.velikov@...labora.com>
> Reviewed-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> Signed-off-by: Maxime Ripard <maxime.ripard@...tlin.com>

Reviewed-by: Philipp Zabel <p.zabel@...gutronix.de>

Just one small suggestion:

[...]
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> index 20a9c296d027..345d5cb5e956 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> @@ -317,21 +317,18 @@ static void scl_vop_cal_scl_fac(struct vop *vop, const struct vop_win_data *win,
>  			     uint32_t src_w, uint32_t src_h, uint32_t dst_w,
>  			     uint32_t dst_h, uint32_t pixel_format)
>  {
> +	const struct drm_format_info *info = drm_format_info(pixel_format);

The only call site in vop_plane_atomic_update passes fb->format->format
as pixel_format parameter, so this could be simplified even further by
replacing the uint32_t pixelformat argument with a const struct
drm_format_info *info, and passing fb->format directly instead.

regards
Philipp