linux-kernel - Re: [PATCH] drm/stm: ltdc: add clut mode support

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Date:   Sun, 12 Nov 2017 13:31:10 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Philippe CORNU <philippe.cornu@...com>,
        Yannick FERTRE <yannick.fertre@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Vincent ABRIOU <vincent.abriou@...com>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Fabien DESSENNE <fabien.dessenne@...com>,
        Mickael REULIER <mickael.reulier@...com>,
        Gabriel FERNANDEZ <gabriel.fernandez@...com>,
        Ludovic BARRE <ludovic.barre@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>
Subject: Re: [PATCH] drm/stm: ltdc: add clut mode support

On 2017-11-10 17:12, Philippe CORNU wrote:
> Hi Peter,
> 
> On 11/07/2017 05:34 PM, Peter Rosin wrote:
>> On 2017-11-07 16:53, Philippe CORNU wrote:
>>> + Peter
>>>
>>> Hi Peter,
>>>
>>> CLUT support on STM32 has been removed thanks to your clean up patch
>>
>> Support is a bit strong for what I thought was a dead function, or
>> are you saying that it used to work before my series? Really sorry
>> if that is the case!
> 
> As I wrote in the previous related thread 
> (https://lists.freedesktop.org/archives/dri-devel/2017-June/145070.html), 
> STM32 chipsets supports 8-bit CLUT mode but this driver version does not 
> support it "yet"...
> 
> So, no worry regarding your clean up, I gave you an "acked-by" for that : )

Ok, good. Thanks for clearing that up!

>>
>> Anyway, the function I removed seemed to indicate that the hardware
>> could handle a separate clut for each layer, but your new version
>> does not. Why is that?
> 
> Yes I confirm the clut support is available for each layer... but I 
> thought the gamma_lut was only at the crtc level, not at layer level... 
> Maybe I am wrong.
> Moreover, small test applications I used play only with clut at crtc 
> level...
> 
> Anyway, could you please help me to "find" a per-layer clut 
> implementation because when I read "crtc->state->gamma_lut->data" it 
> looks like gamma_lut is per crtc, not per plane...? or maybe I have to 
> add extra properties for that...

I wasn't clear enough. Yes, there is to my knowledge only one clut,
not one per plane. What I noticed was that the function I removed
seemed to touch clut registers for multiple layers, but your new
function appears to only touch registers for one layer. So, I
wondered if the "one and only" clut needed to be copied to the
registers for the other layers, or if the old dead code was simply
confused. Clearer?

Cheers.
Peter