linux-kernel - Re: [PATCH 10/10] drm/tidss: Fix atomic

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Date:   Wed, 1 Nov 2023 16:56:58 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     Aradhya Bhatia <a-bhatia1@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jyri Sarha <jyri.sarha@....fi>,
        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>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] drm/tidss: Fix atomic_flush check

Hi Tomi,

Thank you for the patch.

On Wed, Nov 01, 2023 at 11:17:47AM +0200, Tomi Valkeinen wrote:
> tidss_crtc_atomic_flush() checks if the crtc is enabled, and if not,
> returns immediately as there's no reason to do any register changes.
> 
> However, the code checks for 'crtc->state->enable', which does not
> reflect the actual HW state. We should instead look at the
> 'crtc->state->active' flag.
> 
> This causes the tidss_crtc_atomic_flush() to proceed with the flush even
> if the active state is false, which then causes us to hit the
> WARN_ON(!crtc->state->event) check.
> 
> Fix this by checking the active flag, and while at it, fix the related
> debug print which had "active" and "needs modeset" wrong way.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> ---
>  drivers/gpu/drm/tidss/tidss_crtc.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_crtc.c b/drivers/gpu/drm/tidss/tidss_crtc.c
> index 5e5e466f35d1..4c7009a5d643 100644
> --- a/drivers/gpu/drm/tidss/tidss_crtc.c
> +++ b/drivers/gpu/drm/tidss/tidss_crtc.c
> @@ -169,13 +169,12 @@ static void tidss_crtc_atomic_flush(struct drm_crtc *crtc,
>  	struct tidss_device *tidss = to_tidss(ddev);
>  	unsigned long flags;
>  
> -	dev_dbg(ddev->dev,
> -		"%s: %s enabled %d, needs modeset %d, event %p\n", __func__,
> -		crtc->name, drm_atomic_crtc_needs_modeset(crtc->state),
> -		crtc->state->enable, crtc->state->event);
> +	dev_dbg(ddev->dev, "%s: %s active %d, needs modeset %d, event %p\n",
> +		__func__, crtc->name, crtc->state->active,
> +		drm_atomic_crtc_needs_modeset(crtc->state), crtc->state->event);

While at it, how about this ?

	dev_dbg(ddev->dev, "%s: %s is %sactive, %s modeset, event %p\n",
		__func__, crtc->name, crtc->state->active ? "" : "not ",
		drm_atomic_crtc_needs_modeset(crtc->state) ? "needs", "doesn't need",
		crtc->state->event);

>  
>  	/* There is nothing to do if CRTC is not going to be enabled. */
> -	if (!crtc->state->enable)
> +	if (!crtc->state->active)

I think the drm_atomic_helper_commit_planes() helper will handle this if
you pass it the DRM_PLANE_COMMIT_ACTIVE_ONLY flag.

>  		return;
>  
>  	/*

-- 
Regards,

Laurent Pinchart