linux-kernel - Re: [PATCH] drm/vblank: Simplify drm_dev_has

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Date:   Wed, 5 Apr 2023 10:10:15 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/vblank: Simplify drm_dev_has_vblank()

On Wed, Apr 05, 2023 at 12:00:23AM +0300, Ville Syrjälä wrote:
> On Tue, Apr 04, 2023 at 10:46:00PM +0200, Daniel Vetter wrote:
> > On Mon, Apr 03, 2023 at 09:07:35AM -0700, Rob Clark wrote:
> > > From: Rob Clark <robdclark@...omium.org>
> > > 
> > > What does vblank have to do with num_crtcs?  Well, this was technically
> > > correct, but you'd have to go look at where num_crtcs is initialized to
> > > understand why.  Lets just replace it with the simpler and more obvious
> > > check.
> > 
> > If you want to fix this, then I think the right fix is to rename num_crtcs
> > to be something like num_vblank_crtcs. It's a historical accident back
> > when vblanks without kms was a thing.
> > 
> > Plan B is someone gets really busy and fixes up the entire vblank mess and
> > moves it into drm_crtc struct. Now that the dri1 drivers are gone we could
> > indeed do that.
> 
> And easy first step could to simply wrap all the naked
> &dev->vblank[drm_crtc_index()] things into a function
> call with some cocci/etc. That way most of the vblank
> code doesn't need to care where that thing actually lives.

Yeah I think that might work out. Roughly:
- Wrap all the drm_vblank_crtc lookups
- Emebed it into drm_crtc, delete the drm_device->vblank array
- rename drm_device->num_crtc to something more meaningful maybe and move
  into drm_modeset_config

The big holdup always was step 2 because we still had to care about legacy
drivers without drm_crtc, which meant you'd have to have two paths, which
was kinda really annoying.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch