linux-kernel - Re: [PATCH] drm: atmel-hlcdc: use a default gamma ramp if none is specified

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Date:   Mon, 3 Jul 2017 13:31:02 +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>,
        dri-devel@...ts.freedesktop.org,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH] drm: atmel-hlcdc: use a default gamma ramp if none is
 specified

On Mon,  3 Jul 2017 11:42:10 +0200
Peter Rosin <peda@...ntia.se> wrote:

> At init and if the gamma_lut property is ever removed, the clut
> registers must be programmed with a default gamma ramp instead of
> being left in some unknown state.
> 
> Fixes: 364a7bf574eb ("drm: atmel-hlcdc: add support for 8-bit color lookup table mode")
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> index b5bd9b0..0ccd93c 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> @@ -429,6 +429,14 @@ static void atmel_hlcdc_plane_update_format(struct atmel_hlcdc_plane *plane,
>  				    ATMEL_HLCDC_LAYER_FORMAT_CFG, cfg);
>  }
>  
> +static void atmel_hlcdc_default_gamma_ramp(struct atmel_hlcdc_layer *layer)
> +{
> +	int idx;
> +
> +	for (idx = 0; idx < ATMEL_HLCDC_CLUT_SIZE; idx++)
> +		atmel_hlcdc_layer_write_clut(layer, idx, idx * 0x10101);
> +}
> +
>  static void atmel_hlcdc_plane_update_clut(struct atmel_hlcdc_plane *plane)
>  {
>  	struct drm_crtc *crtc = plane->base.crtc;
> @@ -438,9 +446,14 @@ static void atmel_hlcdc_plane_update_clut(struct atmel_hlcdc_plane *plane)
>  	if (!crtc || !crtc->state)
>  		return;
>  
> -	if (!crtc->state->color_mgmt_changed || !crtc->state->gamma_lut)
> +	if (!crtc->state->color_mgmt_changed)
>  		return;
>  
> +	if (!crtc->state->gamma_lut) {
> +		atmel_hlcdc_default_gamma_ramp(&plane->layer);

Hm, I'd prefer to have state->gamma_lut properly initialized in
atmel_hlcdc_crtc_reset(), this way you don't have to do that in the
update path.

> +		return;
> +	}
> +
>  	lut = (struct drm_color_lut *)crtc->state->gamma_lut->data;
>  
>  	for (idx = 0; idx < ATMEL_HLCDC_CLUT_SIZE; idx++, lut++) {
> @@ -918,6 +931,8 @@ static int atmel_hlcdc_plane_init_properties(struct atmel_hlcdc_plane *plane,
>  					    0x40040890);
>  	}
>  
> +	atmel_hlcdc_default_gamma_ramp(&plane->layer);
> +
>  	return 0;
>  }
>