Re: [linux-sunxi] Re: [PATCH v7 05/13] drm/sun4i: abstract a engine type

[Maxime Ripard <maxime.ripard@free-electrons.com>]

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On Mon, May 15, 2017 at 05:35:02PM +0800, Icenowy Zheng wrote:
> 
> 
> 于 2017年5月15日 GMT+08:00 下午5:20:01, Maxime Ripard <maxime.ripard@free-electrons.com> 写到:
> >On Mon, May 15, 2017 at 12:30:37AM +0800, Icenowy Zheng wrote:
> >> As we are going to add support for the Allwinner DE2 engine in
> >sun4i-drm
> >> driver, we will finally have two types of display engines -- the DE1
> >> backend and the DE2 mixer. They both do some display blending and
> >feed
> >> graphics data to TCON, and is part of the "Display Engine" called by
> >> Allwinner, so I choose to call them both "engine" here.
> >> 
> >> Abstract the engine type to a new struct with an ops struct, which
> >contains
> >> functions that should be called outside the engine-specified code (in
> >> TCON, CRTC or TV Encoder code).
> >> 
> >> Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
> >> Reviewed-by: Chen-Yu Tsai <wens@csie.org>
> >> ---
> >> Changes in v7:
> >> - Mention "Display Engine" for the name "engine".
> >> - Fixed some small issues found by Chen-Yu and added his ACK.
> >> Changes in v6:
> >> - Rebased on wens's multi-pipeline patchset.
> >> - Split out Makefile changes.
> >
> >You also added a get_id callback here...
> >
> >> +static const struct sunxi_engine_ops sun4i_backend_engine_ops = {
> >> +	.commit				= sun4i_backend_commit,
> >> +	.layers_init			= sun4i_layers_init,
> >> +	.apply_color_correction		= sun4i_backend_apply_color_correction,
> >> +	.disable_color_correction	= sun4i_backend_disable_color_correction,
> >> +};
> >> +
> >
> >... that you don't populate ...
> >
> >> @@ -477,7 +481,7 @@ static int sun4i_tcon_bind(struct device *dev,
> >struct device *master,
> >>  	dev_set_drvdata(dev, tcon);
> >>  	tcon->drm = drm;
> >>  	tcon->dev = dev;
> >> -	tcon->id = backend->id;
> >> +	tcon->id = sunxi_engine_get_id(engine);
> >
> >... that you call to fill the TCON ID ...
> >
> >> +/**
> >> + * sunxi_engine_get_id - Get the ID of the engine.
> >> + * @engine:	pointer to the engine
> >> + *
> >> + * If the ID is not necessary, just do not implement it in
> >sunxi_engine_ops,
> >> + * and a default -1 will be returned.
> >> + */
> >> +static inline int
> >> +sunxi_engine_get_id(struct sunxi_engine *engine)
> >> +{
> >> +	if (engine->ops && engine->ops->get_id)
> >> +		return engine->ops->get_id(engine);
> >> +
> >> +	return -1;
> >
> >... and will return -1 if not populated, which essentially means that
> >instead of having 0 or 1, we're now having -1 as our id.
> >
> >This is a regression, and I'm even wondering if we can't just store
> >the ID in the sunxi_engine structure. Is anything preventing us to do
> >that, instead of using a callback?
> 
> Some engines (de2 mixer) doesn't use the ID. But 0 is a valid ID here.

Surely it will at some point.

> If we just store it in sunxi_engine, it should be assigned -1 for de2 mixer.
> Is this applicable?
> 
> If it's okay I will do so.

Yes, it sounds reasonable.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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