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

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Date: Wed, 20 Mar 2024 19:59:13 +0100
From: Mehdi Djait <mehdi.djait.k@...il.com>
To: Javier Martinez Canillas <javierm@...hat.com>
Cc: Thomas Zimmermann <tzimmermann@...e.de>, 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 ?

Hello Javier, Hello Thomas,

On Tue, Mar 19, 2024 at 09:52:34AM +0100, Javier Martinez Canillas wrote:
> 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.

Thank you both very much!

--
Kind Regards
Mehdi Djait