[PATCH] drm/stm: ltdc: add clut mode support

[Peter Rosin]

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