linux-kernel - Re: [PATCH] drm/ssd130x: Replace simple display helpers with the atomic helpers

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Date:   Mon, 5 Sep 2022 13:55:01 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/ssd130x: Replace simple display helpers with the
 atomic helpers

On 9/5/22 13:34, Thomas Zimmermann wrote:

[...]

>>>
>>
>> Yes, I was abusing the concept of encoder here just to have a place where
>> I could hook the enable / disable logic, since I was looking at the other
>> DRM objects helper operations structures and found that these were only
>> defined for the encoder.
> 
> I liked the idea of handling backlighting here. Power on/off also seems 
> sensible.
>

Ok. I'll keep that then.
 
>>
>> But there is technically no encoder on this device. As you can see, I was
>> using DRM_MODE_ENCODER_NONE when the encoder is initialized.
>>
>> But I notice now that the struct drm_crtc_helper_funcs also have .enable
>> and .disable callbacks, it seems I was just blind and didn't see before.
> 
> You certainly want to use atomic_enable/atomic_disable. They are 
> mutually exclusive with the other enable/disable functions.
> 

Ah, then I wasn't blind after all. It was because the encoder was the
only DRM object that had .atomic_{en,dis}able. The CRTC only had some
.{en,disable} helper callbacks.

>>
>> Would having the init and poweroff logic in the CRTC helpers be correct
>> to you or was do you have in mind ?
> 
> There's quite a bit happening in the init function. Does it have to be 
> re-initialized on each enable operation?  If it survives the power-off 
> call, the initial init can be done in the CRTC reset function. It's 
> purpose is to set hardware and software to a clean state.
>

I need to check if it survives a disable/enable cycle. Specially since
on disable the VCC regulator is disabled, which might lead to the chip
state to get lost.
 
> Best regards
> Thomas
> 
>>
>>> Best regards
>>> Thomas
> 

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat