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

[Icenowy Zheng]

于 2017年5月15日 GMT+08:00 下午5:20:01, Maxime Ripard <maxime.ripard at 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 at aosc.io>
>> Reviewed-by: Chen-Yu Tsai <wens at 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.

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.

>
>Maxime