Re: [PATCH 00/22] drm: Convert drivers to drm_simple_encoder_init()

[Sam Ravnborg <sam@ravnborg.org>]

Hi Thomas.

On Fri, Mar 06, 2020 at 04:18:52PM +0100, Thomas Zimmermann wrote:
> Hi Laurent
> 
> Am 06.03.20 um 15:22 schrieb Laurent Pinchart:
> > Hi Thomas,
> > 
> > Thank you for the patch.
> > 
> > On Thu, Mar 05, 2020 at 04:59:28PM +0100, Thomas Zimmermann wrote:
> >> A call to drm_simple_encoder_init() initializes an encoder without
> >> further functionality. It only provides the destroy callback to
> >> cleanup the encoder's state. Only few drivers implement more
> >> sophisticated encoders than that. Most drivers implement such a
> >> simple encoder and can use drm_simple_encoder_init() instead.
> >>
> >> The patchset converts drivers where the encoder's instance is
> >> embedded in a larger data structure. The driver releases the
> >> memory during cleanup. Each patch replaces drm_encoder_init() with
> >> drm_simple_encoder_init() and removes the (now unused) driver's
> >> encoder functions.
> >>
> >> While the patchset is fairly large, the indiviual patches are self-
> >> contained and can be merged independently from each other. The
> >> simple-encoder functionality is currently in drm-misc-next, where
> >> these patches could go as well.
> > 
> > I've reviewed the whole series, including verifying that the few
> > instances of struct drm_encoder_funcs that were not declared const were
> > not modified somewhere to add more function pointers.
> > 
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> Thanks for the detailed review.
> 
> > 
> > for all the patches.
> > 
> > However, I'd like to note that drm_simple_encoder_init() is a bit of a
> > misnommer here. Several of the encoders in those drivers to implement
> > additional functionality. They just expose them through
> > drm_encoder_helper_funcs, not drm_encoder_funcs.
> 
> True. It's called 'simple encoder' for the lack of a better name. It's
> part of the simple KMS helpers, so the name's at least consistent. OTOH
> I always find drm_simple_display_pipe a bad name.
> 
> We can still rename the simple-encoder function without much effort. I'm
> open for suggestions.

IMO this does not belong in drm_simple_kms - but in drm_encoder.
This only occurs to me after looking a bit more on the patches,
you would have loved to get this feedback earlier.

Most users do not need their owm drm_encoder_funcs definition,
and would be happy with the default as provided by drm_simple_*

As the cleanup is handled automatically when the drm device
is teared down (in mode_config_rest()) I considered if we could here
use the drmm_ namespace - but that felt wrong.

My proposal is the following:
- Move the implementation to drm_encoder.c
- Name it drm_encoder_init_nofuncs()

The patches posted in this thread would be a little simpler
as they would loose the added include file.
And the three drivers using the current infrastructure would need a
small update.

I you decide to keep the current approach where the
functions are in drm_simple_* then the full series is:
Acked-by: Sam Ravnborg <sam@ravnborg.org>

But I think moving it to drm_encoder.c would be the approach that would
make it simpler to understand/follow. So that get my (biased) vote.

	Sam

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