linux-kernel - Re: drm/tiny: QUESTION: What to use instead of drm_simple_display

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Date: Tue, 19 Mar 2024 09:52:34 +0100
From: Javier Martinez Canillas <javierm@...hat.com>
To: Thomas Zimmermann <tzimmermann@...e.de>, Mehdi Djait
 <mehdi.djait.k@...il.com>, daniel@...ll.ch,
 maarten.lankhorst@...ux.intel.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: drm/tiny: QUESTION: What to use instead of
 drm_simple_display_pipe ?

Thomas Zimmermann <tzimmermann@...e.de> writes:

Hello Mehdi,

> Hi
>
> Am 18.03.24 um 20:18 schrieb Mehdi Djait:
>> Hello everyone :)
>>
>> I am implementing a tiny drm driver and I am currently working on the
>> V2: https://lore.kernel.org/dri-devel/cover.1701267411.git.mehdi.djait@bootlin.com/
>>
>> I got a review on the v1 telling me not to use the
>> drm_simple_display_pipe. Can someone please explain this further ? Or
>> give me an example drm driver that does it the right way ?
>
> You can copy the code from drm_simple_kms_helper.c into your driver file 
> and start inlining everything. For example
>
>   1) Your driver calls drm_simple_display_pipe_init(), so you copy that 
> code into your source file
>   2) drm_simple_display_pipe_init() uses drm_simple_kms_plane_funcs and 
> drm_simple_kms_crtc_funcs, so you copy these into your source file; 
> together with the drm_simple_kms_*() helpers that they use for their 
> callback pointers.
>   3) Mayb do this for other drm_simple_kms_*() code.
>   4) Then start inlining: inline your copy of 
> drm_simple_display_pipe_iit(). Instead of using 
> sharp_ls027b7dh01_pipe_funcs, inline its functions into your copy of the 
> callers. And so on.
>   5) Rename the resulting code, so that it fits you driver.
>
> With careful changes, you 'll end up with the same functionality as 
> before, but without the intermediate layer of the simple-KMS code.
>

On top of what Thomas said, you can check 622113b9f11f ("drm/ssd130x:
Replace simple display helpers with the atomic helpers") that did this
change for the drivers/gpu/drm/solomon/ssd130x.c driver.

The driver is also for a monochrome panel controller and it does support
SPI as transport, which means the controller is similar to yours in many
aspects. You could use that driver code as a reference for your driver.

> Best regards
> Thomas
>
>>
>> --
>> Kind Regards
>> Mehdi Djait
>
> -- 
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat