Re: [PATCH v3 04/10] drm/fbdev-generic: Initialize fb-helper structure in generic setup

From: Sam Ravnborg <sam@ravnborg.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
Cc: airlied@gmail.com, daniel@ffwll.ch,
	maarten.lankhorst@linux.intel.com, mripard@kernel.org,
	javierm@redhat.com, linux-samsung-soc@vger.kernel.org,
	linux-arm-msm@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
	linux-tegra@vger.kernel.org, freedreno@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 04/10] drm/fbdev-generic: Initialize fb-helper structure in generic setup
Date: Fri, 27 Jan 2023 18:35:18 +0100	[thread overview]
Message-ID: <Y9QLVmyRvSVxQywz@ravnborg.org> (raw)
In-Reply-To: <441188d8-01a6-2a48-ce46-e32d7006aafa@suse.de>

On Fri, Jan 27, 2023 at 03:21:30PM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 25.01.23 um 22:03 schrieb Sam Ravnborg:
> > Hi Thomas,
> > 
> > On Wed, Jan 25, 2023 at 09:04:09PM +0100, Thomas Zimmermann wrote:
> > > Initialize the fb-helper structure immediately after its allocation
> > > in drm_fbdev_generic_setup(). That will make it easier to fill it with
> > > driver-specific values, such as the preferred BPP.
> > > 
> > > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> > > Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> > > ---
> > >   drivers/gpu/drm/drm_fbdev_generic.c | 13 +++++++++----
> > >   1 file changed, 9 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c
> > > index 135d58b8007b..63f66325a8a5 100644
> > > --- a/drivers/gpu/drm/drm_fbdev_generic.c
> > > +++ b/drivers/gpu/drm/drm_fbdev_generic.c
> > > @@ -385,8 +385,6 @@ static int drm_fbdev_client_hotplug(struct drm_client_dev *client)
> > >   	if (dev->fb_helper)
> > >   		return drm_fb_helper_hotplug_event(dev->fb_helper);
> > > -	drm_fb_helper_prepare(dev, fb_helper, &drm_fb_helper_generic_funcs);
> > > -
> > >   	ret = drm_fb_helper_init(dev, fb_helper);
> > >   	if (ret)
> > >   		goto err;
> > 
> >  From the documentation:
> > The drm_fb_helper_prepare()
> > helper must be called first to initialize the minimum required to make
> > hotplug detection work.
> > ...
> > To finish up the fbdev helper initialization, the
> > drm_fb_helper_init() function is called.
> > 
> > So this change do not follow the documentation as drm_fb_helper_init()
> > is now called before drm_fb_helper_prepare()
> 
> No, we now call drm_fb_helper_prepare() from within
> drm_fbdev_generic_setup(), right after allocating the fb_helper.
> drm_fb_helper_init() will only be called after the client received a
> hot-plug event.
> 
> > 
> > I did not follow all the code - but my gut feeling is that the
> > documentation is right.
> 
> The docs are of low quality. The _prepare() helper is the actual init
> function and _init() only sets the fb_helper in the device instance.
OK, thanks for the follow-up.


	Sam

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