linux-kernel - Re: [PATCH v3 2/3] drm/fb-cma-helper: expose more of fb cma guts

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Date:   Mon, 19 Jun 2017 22:41:06 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 2/3] drm/fb-cma-helper: expose more of fb cma guts

Le Mon, 19 Jun 2017 09:44:25 +0200,
Peter Rosin <peda@...ntia.se> a écrit :

> DRM drivers supporting clut may want a convenient way to only use
> non-default .gamma_set and .gamma_get ops in the drm_fb_helper_funcs
> in order to avoid the following
> 
> 	/*
> 	 * The driver really shouldn't advertise pseudo/directcolor
> 	 * visuals if it can't deal with the palette.
> 	 */
> 	if (WARN_ON(!fb_helper->funcs->gamma_set ||
> 		    !fb_helper->funcs->gamma_get))
> 		return -EINVAL;
> 
> warning in drm_fb_helper.c:setcolreg().

Did you read the FIXME in the struct doc [1]? Shouldn't we try to move
to this generic approach instead of exposing fb_cma internals? You
could probably mimic (or re-use) what's done in
drm_mode_gamma_set/get_ioctl() [2].

[1]http://elixir.free-electrons.com/linux/v4.12-rc6/source/include/drm/drm_fb_helper.h#L110
[2]http://elixir.free-electrons.com/linux/v4.12-rc6/source/drivers/gpu/drm/drm_color_mgmt.c#L214