linux-kernel - Re: [PATCH] drm/vkms: add support for gamma

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Date:   Mon, 31 Aug 2020 11:39:10 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Sidong Yang <realwakka@...il.com>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Emil Velikov <emil.l.velikov@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Melissa Wen <melissa.srw@...il.com>
Subject: Re: [PATCH] drm/vkms: add support for gamma_set interface

On Saturday, August 29, 2020 4:06 PM, Sidong Yang <realwakka@...il.com> wrote:

> Currently vkms module doesn't support gamma function for userspace. so igt
> subtests in kms_plane(pixel-format-pipe-A-plan) failed for calling
> drmModeCrtcSetGamma().

It doesn't seem like this IGT test's goal is to exercise support for
gamma LUTs. Does the test just tries to reset the gamma LUT to linear?
If so, I think the IGT test should be fixed to ignore "I don't support
gamma" errors.

> This patch set gamma_set interface in vkms_crtc_funcs for
> support gamma function. With initializing crtc, added calls for setting gamma
> size. it pass the test after this patch.
>
> Cc: Daniel Vetter<daniel@...ll.ch>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> Cc: Haneen Mohammed <hamohammed.sa@...il.com>
>
> Signed-off-by: Sidong Yang <realwakka@...il.com>
> ---
>  drivers/gpu/drm/vkms/vkms_crtc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index ac85e17428f8..643435fb2ee6 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -160,6 +160,7 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
>  	.get_crc_sources	= vkms_get_crc_sources,
>  	.set_crc_source		= vkms_set_crc_source,
>  	.verify_crc_source	= vkms_verify_crc_source,
> +	.gamma_set		= drm_atomic_helper_legacy_gamma_set,

Why does VKMS need to use a legacy helper?

It seems like this patch just advertises support for gamma LUTs, but
ignores any value set by user-space. If VKMS advertises support for
gamma LUTs, it needs to take the LUT into account when blending planes.

>  };
>
>  static int vkms_crtc_atomic_check(struct drm_crtc *crtc,
> @@ -275,6 +276,13 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>  		return ret;
>  	}
>
> +	ret = drm_mode_crtc_set_gamma_size(crtc, 256);
> +	if (ret) {
> +		DRM_ERROR("Failed to set gamma size\n");
> +		return ret;
> +	}
> +	drm_crtc_enable_color_mgmt(crtc, 0, false, 256);
> +
>  	drm_crtc_helper_add(crtc, &vkms_crtc_helper_funcs);
>
>  	spin_lock_init(&vkms_out->lock);
> --
> 2.17.1