linux-kernel - Re: [PATCH] drm: writeback: Introduce drm managed helpers

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Message-ID: <ZvE68e95dwLqjVuW@2a02-8440-b157-69df-aafc-5046-a3b3-4ce9.rev.sfr.net>
Date: Mon, 23 Sep 2024 11:54:57 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	jani.nikula@...ux.intel.com, thomas.petazzoni@...tlin.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: writeback: Introduce drm managed helpers

Le 22/09/24 - 18:31, Dmitry Baryshkov a écrit :
> On Fri, Sep 06, 2024 at 07:28:17PM GMT, Louis Chauvet wrote:
> > Currently drm_writeback_connector are created by
> > drm_writeback_connector_init or drm_writeback_connector_init_with_encoder.
> > Both of the function uses drm_connector_init and drm_encoder_init, but
> > there is no way to properly clean those structure from outside. By using
> > drm managed variants, we can ensure that the writeback connector is
> > properly cleaned.
> > 
> > This patch introduce drmm_writeback_connector_init, an helper to initialize
> > a writeback connector using drm managed helpers. This function allows the
> > caller to use its own encoder.
> 
> Also it introduces drm_writeback_connector_cleanup(). Ideally that
> should be a separate commit with a proper description.

Will do for the v2.

> You should also
> document that existing users should call that function (and maybe add a
> WARN_ON that can check if the function wasn't called).

It was my initial implementation [2] (usage in [3]), but Maxime suggested 
switching to drmm. If I make it non-static, this will be a new API with no 
user.

I don't know how to add a warning if this function is not called. Do you 
have an example somewhere where a warning is emitted after everything has 
been cleaned up?

> Last, but not least, please don't add API without a user. Please switch
> at least one driver into using this API.

The user will be VKMS, see [1].

[1]:https://lore.kernel.org/all/20240912-google-vkms-managed-v3-4-7708d6ad262d@bootlin.com/
[2]:https://lore.kernel.org/all/20240814-google-remove-crtc-index-from-parameter-v1-11-6e179abf9fd4@bootlin.com/
[3]:https://lore.kernel.org/all/20240814-google-remove-crtc-index-from-parameter-v1-12-6e179abf9fd4@bootlin.com/

Thanks,
Louis Chauvet

> > 
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > ---
> > Hi Maxime, Jani,
> > 
> > I tried with this commit to implement the drm-managed version of writeback 
> > connector initialization. I tested with the current vkms driver, and it 
> > seems to works (at least no crash/warns).
> > 
> > As suggested by Jani, I only created one function, which takes a 
> > NULL-able pointer for encoder/encoder functions/possible_crtc. What do you 
> > think about it?
> > 
> > Regarding the documentation, I think I repeated too much, can I simply add 
> > comments like "see documentation of @... for the details / requirements"?
> > 
> > Good weekend,
> > Louis Chauvet
> > ---
> >  drivers/gpu/drm/drm_writeback.c | 224 ++++++++++++++++++++++++++++++++++------
> >  include/drm/drm_writeback.h     |   7 ++
> >  2 files changed, 201 insertions(+), 30 deletions(-)
> > 
> 
> -- 
> With best wishes
> Dmitry