Re: [PATCH v5 01/23] drm/encoder: Add of_graph port to struct drm_encoder

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 09 Feb 2022, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> David, Daniel,
>
> I'll need a word from you regarding this patch. It's needed in patch
> 22/23 in this series.
> vop2_crtc_atomic_enable() needs to control the mux which routes the
> display output to the different encoders. Which encoder is used is
> described in the of_graph port, so I need a way to identify the encoder
> in the device tree.

I think the question is how useful is this going to be in general. IMO
we should not be adding members that are useful in a single driver only.

For example i915 wraps encoders with:

	struct intel_encoder {
		struct drm_encoder base;

		/* i915 specific stuff here*/
	};

So that we can add stuff of our own there. Of course, it does mean a
bunch of overhead for the first time you need to do it. But adding
driver specific stuff to struct drm_encoder adds overhead for everyone.

All that said, *I* don't know how useful the port member would be in
drivers that use device tree. Maybe it's worth it.

BR,
Jani.

>
> Sascha
>
> On Wed, Feb 09, 2022 at 10:53:28AM +0100, Sascha Hauer wrote:
>> Add a device node to drm_encoder which corresponds with the port node
>> in the DT description of the encoder. This allows drivers to find the
>> of_graph link between a crtc and an encoder.
>> 
>> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
>> ---
>>  include/drm/drm_encoder.h | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h
>> index 6e91a0280f31..3acd054b1eb3 100644
>> --- a/include/drm/drm_encoder.h
>> +++ b/include/drm/drm_encoder.h
>> @@ -99,6 +99,8 @@ struct drm_encoder {
>>  	struct drm_device *dev;
>>  	struct list_head head;
>>  
>> +	struct device_node *port;
>> +
>>  	struct drm_mode_object base;
>>  	char *name;
>>  	/**
>> -- 
>> 2.30.2
>> 
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center

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