[Openpvrsgx-devgroup] CI20/JZ4780 HDMI (was Re: Status & HW to bring)

Paul Boddie paul at boddie.org.uk
Tue Nov 12 12:15:55 CET 2019


On Monday 11. November 2019 20.54.13 H. Nikolaus Schaller wrote:
> 
> > Am 11.11.2019 um 15:12 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> > 
> >> Am 11.11.2019 um 13:32 schrieb Paul Boddie <paul at boddie.org.uk>:
> >> 
> >> I think there is already an upstream display driver that might be made
> >> suitable:
> >> 
> >> drivers/gpu/drm/ingenic/ingenic-drm.c
> > 
> > This looks really good.
> > 
> > But seems to support jz4740 and jz4725 only.

The hardware involved is not too different across all the JZ series. Maybe the 
JZ4780 (and perhaps JZ4775) has more support for other features, but having 
seen this code in several different forms, I think it could be adapted.

[...]

> >> So, the Ingenic driver would need to be augmented with port/endpoint
> >> support, and there would need to be a way of activating the Synopsys
> >> driver in the device tree. Exactly how the latter should be done remains
> >> a mystery to me at the moment.
> > 
> > It seems to be device tree compatible but has no .compatible. It includes
> > include/drm/drm_of.h and include/linux/of_graph. But there is no
> > config for CONFIG_DRM_DW_HDMI except _AHB_AUDIO and _CEC in
> > arch/arm/configs/imx_v6_v7_defconfig
> > Indeed it seems to be used in or in combination with some i.MX6 SoC?
> > AFAIK the i.MX6 has no internal HDMI encoder, so the connection isn't
> > clear either.

I don't see any i.MX6-related files in any search despite the origins of the 
driver being from work done to support that chipset.

> > Indeed quite confusing so far (and quite deviating from Openpvrsgx but we
> > need some working video output interface on the CI20 board).
> 
> I took the patch set for drivers/gpu/drm/jz4780 and rebased it to v5.4-rc7
> (wasn't difficult).
> 
> As expected, it fails to compile:

[...]

> Interestingly, it also enables the compile of
> drivers/gpu/drm/bridge/synopsys/dw-hdmi.o which it seems to rely on.
> 
> If you want to take a look, I have pushed the non-compiling version:
> 
> http://git.goldelico.com/?p=gta04-kernel.git;a=shortlog;h=refs/heads/work-jz
> 4780-hdmi

I think it might be better to transplant the endpoint elements from the older 
driver (with updates for the latest ways of doing things) into the Ingenic 
driver, together with some feature enhancements. That's my view for today, at 
least!

Paul


More information about the openpvrsgx-devgroup mailing list