[PATCH 2/3] drm: Use state helper instead of CRTC state pointer

[Maxime Ripard]

On Tue, Nov 03, 2020 at 06:28:24PM +0200, Ville Syrjälä wrote:
> On Tue, Nov 03, 2020 at 05:15:51PM +0100, Maxime Ripard wrote:
> > Hi Ville,
> > 
> > On Mon, Nov 02, 2020 at 06:04:06PM +0200, Ville Syrjälä wrote:
> > > On Mon, Nov 02, 2020 at 02:38:33PM +0100, Maxime Ripard wrote:
> > > > Many drivers reference the crtc->pointer in order to get the current CRTC
> > > > state in their atomic_begin or atomic_flush hooks, which would be the new
> > > > CRTC state in the global atomic state since _swap_state happened when those
> > > > hooks are run.
> > > > 
> > > > Use the drm_atomic_get_new_crtc_state helper to get that state to make it
> > > > more obvious.
> > > > 
> > > > This was made using the coccinelle script below:
> > > > 
> > > > @ crtc_atomic_func @
> > > > identifier helpers;
> > > > identifier func;
> > > > @@
> > > > 
> > > > (
> > > > static struct drm_crtc_helper_funcs helpers = {
> > > > 	...,
> > > > 	.atomic_begin = func,
> > > > 	...,
> > > > };
> > > > |
> > > > static struct drm_crtc_helper_funcs helpers = {
> > > > 	...,
> > > > 	.atomic_flush = func,
> > > > 	...,
> > > > };
> > > > )
> > > > 
> > > > @@
> > > > identifier crtc_atomic_func.func;
> > > > identifier crtc, state;
> > > > symbol crtc_state;
> > > > expression e;
> > > > @@
> > > > 
> > > >   func(struct drm_crtc *crtc, struct drm_atomic_state *state) {
> > > >   ...
> > > > - struct tegra_dc_state *crtc_state = e;
> > > > + struct tegra_dc_state *dc_state = e;
> > > >   <+...
> > > > -       crtc_state
> > > > +	dc_state
> > > >   ...+>
> > > >   }
> > > > 
> > > > @@
> > > > identifier crtc_atomic_func.func;
> > > > identifier crtc, state;
> > > > symbol crtc_state;
> > > > expression e;
> > > > @@
> > > > 
> > > >   func(struct drm_crtc *crtc, struct drm_atomic_state *state) {
> > > >   ...
> > > > - struct mtk_crtc_state *crtc_state = e;
> > > > + struct mtk_crtc_state *mtk_crtc_state = e;
> > > >   <+...
> > > > -       crtc_state
> > > > +	mtk_crtc_state
> > > >   ...+>
> > > >   }
> > > 
> > > These reanames seem a bit out of scpe for this patch. But I guess you
> > > needed then to get the rest of the cocci to work on some drivers?
> > 
> > Yeah, those two drivers already had a variable named crtc_state, calling
> > container_of on crtc->state
> > 
> > It was cleaner to me to have an intermediate variable storing the result
> > of drm_atomic_get_new_crtc_state, but then the most obvious name was
> > taken so I had to rename those two variables before doing so.
> > 
> > > The basic idea looks good:
> > > Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > But I guess up to the individual driver folks to bikeshed the variable
> > > naming and whatnot.
> > > 
> > > One thing I spotted is that a few drivers now gained two aliasing crtc
> > > state pointers in the function: one with the drm type, the other with
> > > a driver specific type. That's something we've outlawed in i915 since
> > > it was making life rather confusing. In i915 we now prefer to use only
> > > the i915 specific types in most places.
> > 
> > I didn't spot any of those cases, do you have an example of where it
> > happened?
> 
> eg. ast:
> +       struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state,                               
> +                                                                         crtc);                               
>         struct drm_crtc_state *old_crtc_state = drm_atomic_get_old_crtc_state(state,                           
>                                                                               crtc);                           
>         struct ast_private *ast = to_ast_private(crtc->dev);                                                   
> -       struct ast_crtc_state *ast_crtc_state = to_ast_crtc_state(crtc->state);                                
> +       struct ast_crtc_state *ast_crtc_state = to_ast_crtc_state(crtc_state);       
> 
> So here both 'crtc_state' and 'ast_crtc_state' are basically the same
> thing, which can get a bit confusing especially within larger functions
> with lots of variables. 

Ah, that kind of aliasing, ok. So it's purely an issue with
ergonomics/convenience?

It seems to be a widespread pattern (I know we're using it in vc4 and
sun4i, and from those reworks I've seen a number of drivers doing so).
I'm not entirely sure how we should fix it through coccinelle too :/

Thanks!
Maxime
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