(EXT) HDMI CEC on ODROID-N2+

[Stefan Agner]

Hi Alexander,

On 2022-01-16 11:14, Alexander Stein wrote:
> Hi Stefan,
> 
> Am Samstag, 15. Januar 2022, 14:28:01 CET schrieb Stefan Agner:
>> That assumption turned out to be wrong: I used our mainline based U-Boot
>> 2021.10 instead of the Arch Linux ARM U-Boot, and HDMI CEC continued to
>> work.
> 
> Does the mainstream U-Boot work out of the box? Or does it require some 
> additional configuration?
> 

Yes mainline U-Boot works out of the box. Building it is somewhat
involved since it requires extra firmwares (there are build instructions
in the source tree in board/amlogic/w400/README.odroid-n2).

You need to add a boot script to your boot partition. I used the script
part of the uboot-odroid-n2-mainline package as inspiration [1]. It
needs some adjustments as it seems to try to boot from the root file
system directly (and my setup used the FAT/ext4 setup still).

We carry a single patch which improved reliability booting from eMMC,
see [2].


>> I then moved to 5.15.13 as well to rule out any kernel changes. But
>> still, in our configuration HDMI CEC did not work. I ended up diffing
>> configuration, and noticed that we are using built-in CONFIG_CEC_CORE
>> whereas Arch Linux uses it as a module. To build CONFIG_CEC_CORE as a
>> module I had to change some other configuration from built-in to module,
>> namely:
>>
>> - CONFIG_CEC_CORE=m
>> - CONFIG_DRM_DW_HDMI=m
>> - CONFIG_DRM_MESON=m
>> - CONFIG_DRM_MESON_DW_HDMI=m
>>
>> With that change, HDMI CEC started to work in my builds too!
>>
>> With that change, it also works on Linux 5.10.
>>
>> I guess there is some ordering issue or something which makes it fail
>> when those drivers are built-in? Note that I did not change
>> CONFIG_CEC_MESON_G12A_AO, that driver was already a module before.
> 
> You need all 4 options above to be modules? Or is it maybe enough to set 
> CONFIG_DRM_DW_HDMI_CEC=m? This should make CONFIG_CEC_CORE=m as well, while 
> the other modules are built-in.

In our builds I disabled CONFIG_DRM_DW_HDMI_CEC entirely actually.

It seems that CONFIG_DRM_DW_HDMI is tied to CEC_CORE through this
dependency:

config DRM_DW_HDMI
...
        select CEC_CORE if CEC_NOTIFIER

> I suspect at some point a -EPROBE_DEFER is missing.
> 
> Just FYI: Arch Linux aarch64 kernel config currently lacks some drivers for 
> HDMI audio. See [1].

Thanks for the link, just checked, it seems our kernel configuration
covers those.

--
Stefan

> 
> Best regards,
> Alexander
> 
> [1] https://github.com/archlinuxarm/PKGBUILDs/pull/1864

[1]
https://github.com/archlinuxarm/PKGBUILDs/blob/master/alarm/uboot-odroid-c2-mainline/boot.txt
[2]
https://github.com/home-assistant/operating-system/blob/rel-7/buildroot-external/board/hardkernel/patches/uboot/0001-HACK-mmc-meson-gx-limit-to-24MHz.patch