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

On Wed, 09 Feb 2022, Sascha Hauer [off-list ref] 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:

quoted

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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