linux-kernel - Re: [PATCH v2 13/14] drm: stm: remove dead code and pointless local lut storage

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Date:   Thu, 22 Jun 2017 11:49:34 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Peter Rosin <peda@...ntia.se>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Russell King <linux@...linux.org.uk>,
        Dave Airlie <airlied@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        "Sean Paul" <seanpaul@...omium.org>,
        Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        "Yannick FERTRE" <yannick.fertre@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Vincent ABRIOU <vincent.abriou@...com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "Boris Brezillon" <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH v2 13/14] drm: stm: remove dead code and pointless local
 lut storage



On 06/22/2017 08:06 AM, Peter Rosin wrote:
> The redundant fb helper .load_lut is no longer used, and can not
> work right without also providing the fb helpers .gamma_set and
> .gamma_get thus rendering the code in this driver suspect.
> 

Hi Peter,
STM32 chipsets supports 8-bit CLUT mode but this driver version does not 
support it "yet" (final patch has not been upstreamed because it was a 
too big fbdev patch for simply adding CLUT...).

Regarding your patch below, if it helps you to ease the drm framework 
update then I am agree to "acknowledge it" asap, else if you are not in 
a hurry, I would prefer a better and definitive patch handling 8-bit 
CLUT properly and I am ok to help or/and to do it : )

Extra questions:
- any plan to update modetest with the DRM_FORMAT_C8 support + gamma 
get/set?
- do you have a simple way to test clut with fbdev, last year we where 
using an old version of the SDL but I am still looking for a small piece 
of code to do it (else I will do it myself but C8 on fbdev is not really 
a priority ;-)

best regards,
Philippe

> Just remove the dead code.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>   drivers/gpu/drm/stm/ltdc.c | 12 ------------
>   drivers/gpu/drm/stm/ltdc.h |  1 -
>   2 files changed, 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 1b9483d..87829b9 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -375,17 +375,6 @@ static irqreturn_t ltdc_irq(int irq, void *arg)
>    * DRM_CRTC
>    */
>   
> -static void ltdc_crtc_load_lut(struct drm_crtc *crtc)
> -{
> -	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
> -	unsigned int i, lay;
> -
> -	for (lay = 0; lay < ldev->caps.nb_layers; lay++)
> -		for (i = 0; i < 256; i++)
> -			reg_write(ldev->regs, LTDC_L1CLUTWR + lay * LAY_OFS,
> -				  ldev->clut[i]);
> -}
> -
>   static void ltdc_crtc_enable(struct drm_crtc *crtc)
>   {
>   	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
> @@ -523,7 +512,6 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc *crtc,
>   }
>   
>   static struct drm_crtc_helper_funcs ltdc_crtc_helper_funcs = {
> -	.load_lut = ltdc_crtc_load_lut,
>   	.enable = ltdc_crtc_enable,
>   	.disable = ltdc_crtc_disable,
>   	.mode_set_nofb = ltdc_crtc_mode_set_nofb,
> diff --git a/drivers/gpu/drm/stm/ltdc.h b/drivers/gpu/drm/stm/ltdc.h
> index d7a9c73..620ca55 100644
> --- a/drivers/gpu/drm/stm/ltdc.h
> +++ b/drivers/gpu/drm/stm/ltdc.h
> @@ -27,7 +27,6 @@ struct ltdc_device {
>   	struct drm_panel *panel;
>   	struct mutex err_lock;	/* protecting error_status */
>   	struct ltdc_caps caps;
> -	u32 clut[256];		/* color look up table */
>   	u32 error_status;
>   	u32 irq_status;
>   };
>