Re: HDMI transmitter attachement

[Michael <macallan%netbsd.org@localhost>]

Hello,

On Tue, 16 Sep 2014 12:46:50 +0200
Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote:

> Hello,
> I'm looking for advice about the design for a new driver.
> 
> the AM335x arm SoC includes a framebuffer, which outputs a parallel
> digital video signal. A HDMI transmitter which will serialize this
> video signal can be connected to the SoC, which then allows to
> connect external monitors. The beaglebone black includes a TDA19988
> HDMI transmitter.
> 
> A driver is needed for the TDA19988, to get the EDID from the
> monitor, and also configure the transmitter appropriately. So, in
> addition to the video output lines, the TDA19988 is connected to one
> of the I2C controller of the AM335x (one the beaglebone black it's
> the I2C0 controller, but other boards could use any of the AM335x's
> I2C controllers). In addition, the TDA19988 can transmit a digital
> audio signal, which it gets from the SoC's "multichannel audio serial
> port".
> 
> Now my question is how should the TDA19988 appears in the device
> tree ? I could make it a child of the I2C controller, with the
> framebuffer and audio drivers using ad-hoc callbacks to the TDA19988
> driver. Or I could make it a child of the framebuffer, the
> framebuffer driver redirecting I2C requests to the I2C controller
> driver.
> 
> I think the second solution is less hackish and more flexible;
> but I'd like to hear from people more familiar than I am with
> video hardware and drivers.

I had a similar problem with the valkyriefb driver on macppc - the pixel
clock generator is hooked to an i2c port controlled by cuda, nowhere
near the actual fb's control registers. Got around it ( kinda ) by
having a driver attach to the clock generator ( videopll at iic ... )
and let valkyriefb look for it by name, assuming that there's only one
since it's an onboard device. Maybe some MD, board-specific code should
'know' the wiring and pass the required info as device properties?

have fun
Michael