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

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Date:   Mon, 15 May 2017 11:20:01 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v7 05/13] drm/sun4i: abstract a engine type

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@...c.io>
> Reviewed-by: Chen-Yu Tsai <wens@...e.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?

Maxime

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

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