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

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Date:   Tue, 9 Jan 2018 11:28:01 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Peter Rosin <peda@...ntia.se>,
        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

Hi all,

Do you think the patch is "acceptable" or should I change it somehow?
Any opinion is welcomed : )

Many thanks,
Philippe :-)

On 11/24/2017 02:54 PM, Philippe CORNU wrote:
> Hi Peter,
> 
> On 11/13/2017 11:40 AM, Philippe CORNU wrote:
>> Hi Peter,
>>
>> On 11/12/2017 01:31 PM, Peter Rosin wrote:
>>> 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?
>>>
>>
>> The old code was a generic helper function (ie. for all layers) but 
>> used only for the 1st layer. So, we could say that "old dead code was 
>> simply confused" :-)
>>
>> When I put back the clut support in this patch, I decided to update 
>> only the 1st layer (because there is no API for handling it on other 
>> layers). I also decided to not re-use the former generic helper 
>> function as the update loop is pretty small.
>>
>> This patch offers the clut mode feature for fbdev (only one plane in 
>> fbdev) and for drm (single plane for many use cases, 2nd plane being 
>> used mostly for video...)
>>
>> If tomorrow the API offers clut support per plane, the update loop 
>> will be moved to the plane update function, means the generic helper 
>> function will not be require anymore too.
> 
>  From the explanations above, do you think the patch is "acceptable" or 
> should I change it somehow?
> What is your opinion?
> Many thanks,
> Philippe :-)
> 
>>
>> Many thanks
>> Philippe :)
>>
>>> Cheers.
>>> Peter
>>>