Re: [PATCH] drm/gamma: Clarify gamma lut uapi

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rob Bradford <robert.bradford@intel.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Stefan Schake <stschake@gmail.com>,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Benjamin Gaignard <benjamin.gaignard@linaro.org>,
	Vincent Abriou <vincent.abriou@st.com>,
	amd-gfx@lists.freedesktop.org,
	James Wang <james.qian.wang@arm.com>, CK Hu <ck.hu@mediatek.com>,
	Mali DP Maintainers <malidp@foss.arm.com>,
	Harry Wentland <harry.wentland@amd.com>,
	Daniel Stone <daniels@collabora.com>, Leo Li <sunpeng.li@amd.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Boris Brezillon <bbrezillon@kernel.org>,
	Philippe Cornu <philippe.cornu@st.com>,
	Yannick Fertre <yannick.fertre@st.com>,
	Kausal Malladi <kausalmalladi@gmail.com>,
	Philipp Zabel <p.zabel@pengutronix.de>
Subject: Re: [PATCH] drm/gamma: Clarify gamma lut uapi
Date: Fri, 29 Mar 2019 16:36:05 +0200	[thread overview]
Message-ID: <20190329143605.GB3888@intel.com> (raw)
In-Reply-To: <20190329092027.3430-1-daniel.vetter@ffwll.ch>

On Fri, Mar 29, 2019 at 10:20:27AM +0100, Daniel Vetter wrote:
> Interpreting it as a 0.16 fixed point means we can't accurately
> represent 1.0. Which is one of the values we really should be able to
> represent.
> 
> Since most (all?) luts have lower precision this will only affect
> rounding of 0xffff.
> 
> Cc: Uma Shankar <uma.shankar@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Shashank Sharma <shashank.sharma@intel.com>
> Cc: "Kumar, Kiran S" <kiran.s.kumar@intel.com>
> Cc: Kausal Malladi <kausalmalladi@gmail.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Cc: Rob Bradford <robert.bradford@intel.com>
> Cc: Daniel Stone <daniels@collabora.com>
> Cc: Stefan Schake <stschake@gmail.com>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Leo Li <sunpeng.li@amd.com>
> Cc: amd-gfx@lists.freedesktop.org
> Cc: James (Qian) Wang <james.qian.wang@arm.com>
> Cc: Liviu Dudau <liviu.dudau@arm.com>
> Cc: Mali DP Maintainers <malidp@foss.arm.com>
> Cc: CK Hu <ck.hu@mediatek.com>
> Cc: Philipp Zabel <p.zabel@pengutronix.de>
> Cc: Yannick Fertre <yannick.fertre@st.com>
> Cc: Philippe Cornu <philippe.cornu@st.com>
> Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Cc: Vincent Abriou <vincent.abriou@st.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Boris Brezillon <bbrezillon@kernel.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  include/uapi/drm/drm_mode.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index 09d72966899a..83cd1636b9be 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -621,7 +621,8 @@ struct drm_color_ctm {
>  
>  struct drm_color_lut {
>  	/*
> -	 * Data is U0.16 fixed point format.
> +	 * Values are mapped linearly to 0.0 - 1.0 range, with 0x0 == 0.0 and
> +	 * 0xffff == 1.0.
>  	 */

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  	__u16 red;
>  	__u16 green;
> -- 
> 2.20.1

-- 
Ville Syrjälä
Intel
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