Re: [PATCH] drm: encoder_slave: respect of_node on i2c encoder init

From: Sebastian Hesselbarth
Date: Tue Jun 11 2013 - 17:31:14 EST

On 06/11/2013 05:10 PM, Francisco Jerez wrote:
Sebastian Hesselbarth<sebastian.hesselbarth@xxxxxxxxx> writes:
- I think we could also drop the call to ->set_config since presumably an
of-enabled driver grabbed any required info already from the dt.
I think this way we could still share encoder slaves across tons of
platforms, only the init sequence (and specifically how they get at their

The "set_config" hook is just the way a DRM driver communicates those
board-specific differences in the init sequence to the slave encoder
driver. I don't think it would make sense to remove it unless we make
sure it's being called elsewhere.


for the non-DT case all probe related stuff could be passed with board_info.platform_data. For the DT case, the i2c device driver
will parse properties into .platform_data. IMHO in the end,
.set_config can be safely removed. But for now and especially because
I only have a DT-only platform to test, leave it there and rework
existing drivers and drm master encoders to pass it that way.

IMHO, the whole i2c encoder stuff is just wrong. Not any i2c slave
driver is even really using its probe(). Everything is packed somewhere
because it just worked.. this is at least a start.

Why is that? What do you mean by the probe hooks not being used?
ch7006 and sil164 rely on it being called on initialization.

You are right, I remembered wrong.

I suggest this to get merged to at least allow to have DT slaves,
then start with improving tda998x as an example, then maybe rethink
drm_slave_encoder completely, e.g.

- generalize the concept to SPI attached encoders, "internal" encoders..

drm_encoder_slave is bus-agnostic. drm_i2c_encoder_init() is just a
helper function taking care of bus-specific details like the creation of
the underlying I2C device object, which cannot be made bus-agnostic for
obvious reasons. You're welcome to implement SPI and internal
counterparts of drm_i2c_encoder_init().

Hehe, true again. I like to help and improve it wherever possible. But
to be honest, DRM is not an easy starter for blindly touch commonly
shared functions. If I break Dove, there is little people complaining.
If I also break x86 complaining quickly becomes ranting ;)

- find a way to setup .encoder_type and .connector_type correctly

I guess encoder_type could be initialized correctly from the slave
encoder_init() hook -- that hasn't been necessary until now because the
DRM driver making use of the slave encoder has been expected to have
some other means to find out encoder types [e.g. device-specific BIOS
tables]. OTOH, I don't think that setting connector types is the slave
encoder's business.

Well, I do not completely agree here. Actually, the connector type
cannot be set from any encoder in the chain in a consitent way. But
at least the slave encoder is closer to it.

For Dove (and many other SoCs) the lcd controller is just a dumb rgb
scan-out controller. It makes no difference if you directly connect an
LCD panel or have a HDMI encoder finally connected to an DVI plug.
The LCD controller shouldn't really care because it always sees a dumb
rgb receiver, the HDMI encoder at least can say it is either HDMI or
DVI plug.

For DT, I tend to have a video-card node comprising lcd controllers,
video memory range, external encoder phandle. Maybe put the board-
specific connector here, and then it is up the the master encoder
(or video card "driver") to set the correct connector.

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