linux-kernel - Re: [PATCH v3 06/11] drm: Use state helper instead of plane state pointer in atomic

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Date:   Tue, 23 Feb 2021 15:41:17 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Paul Cercueil <paul@...pouillou.net>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Jyri Sarha <jyri.sarha@....fi>,
        Tomi Valkeinen <tomba@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v3 06/11] drm: Use state helper instead of plane state
 pointer in atomic_check

Hi Thomas,

On Mon, Feb 22, 2021 at 10:12:49AM +0100, Thomas Zimmermann wrote:
> Am 19.02.21 um 13:00 schrieb Maxime Ripard:
> > Many drivers reference the plane->state pointer in order to get the
> > current plane state in their atomic_check hook, which would be the old
> > plane state in the global atomic state since _swap_state hasn't happened
> > when atomic_check is run.
> > 
> > Use the drm_atomic_get_old_plane_state helper to get that state to make
> > it more obvious.
> > 
> > This was made using the coccinelle script below:
> > 
> > @ plane_atomic_func @
> > identifier helpers;
> > identifier func;
> > @@
> > 
> > static struct drm_plane_helper_funcs helpers = {
> > 	...,
> > 	.atomic_check = func,
> > 	...,
> > };
> > 
> > @ replaces_old_state @
> > identifier plane_atomic_func.func;
> > identifier plane, state, plane_state;
> > @@
> > 
> >   func(struct drm_plane *plane, struct drm_atomic_state *state) {
> >   	...
> > -	struct drm_plane_state *plane_state = plane->state;
> > +	struct drm_plane_state *plane_state = drm_atomic_get_old_plane_state(state, plane);
> >   	...
> >   }
> > 
> > @@
> > identifier plane_atomic_func.func;
> > identifier plane, state, plane_state;
> > @@
> > 
> >   func(struct drm_plane *plane, struct drm_atomic_state *state) {
> >   	struct drm_plane_state *plane_state = drm_atomic_get_old_plane_state(state, plane);
> >   	<...
> > -	plane->state
> > +	plane_state
> >   	...>
> >   }
> > 
> > @ adds_old_state @
> > identifier plane_atomic_func.func;
> > identifier plane, state;
> > @@
> > 
> >   func(struct drm_plane *plane, struct drm_atomic_state *state) {
> > +	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> >   	<...
> > -	plane->state
> > +	old_plane_state
> >   	...>
> >   }
> > 
> > @ include depends on adds_old_state || replaces_old_state @
> > @@
> > 
> >   #include <drm/drm_atomic.h>
> > 
> > @ no_include depends on !include && (adds_old_state || replaces_old_state) @
> > @@
> > 
> > + #include <drm/drm_atomic.h>
> >    #include <drm/...>
> > 
> > Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> 
> Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
> 
> However, I find 'old plane state' somewhat confusing in this context,
> because it's actually the current plane state. Would it make sense to use
> drm_atomic_get_existing_plane_state() instead?

drm_atomic_get_existing_plane_state is deprecated nowadays, in favour of either
drm_atomic_get_old_plane_state or drm_atomic_get_new_plane_state

Maxime

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