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

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Message-ID: <ZCyMiERvNHTP45o8@phenom.ffwll.local>
Date:   Tue, 4 Apr 2023 22:46:00 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Rob Clark <robdclark@...il.com>
Cc:     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>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/vblank: Simplify drm_dev_has_vblank()

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.

Or maybe instead a patch to improve the kerneldoc for drm_dev->num_crtc?
-Daniel

> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/drm_vblank.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 877e2067534f..ad34c235d853 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -575,7 +575,7 @@ EXPORT_SYMBOL(drm_vblank_init);
>   */
>  bool drm_dev_has_vblank(const struct drm_device *dev)
>  {
> -	return dev->num_crtcs != 0;
> +	return !!dev->vblank;
>  }
>  EXPORT_SYMBOL(drm_dev_has_vblank);
>  
> -- 
> 2.39.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch