(EXT) HDMI CEC on ODROID-N2+

[Stefan Agner]

Hi Alexander, Hi Neil,

On 2022-01-15 11:52, Stefan Agner wrote:
> Hi Alexander,
> 
> On 2022-01-15 11:02, Alexander Stein wrote:
>> Hi Stefan,
>>
>> Am Donnerstag, 13. Januar 2022, 15:36:38 CET schrieb Stefan Agner:
>>> Hi Neil,
>>>
>>> I am trying to use HDMI CEC on ODROID-N2+ using Linux 5.10.91. However,
>>> I was unsuccessful: As far as I can tell cec-client uses the right
>>> device (I disabled CONFIG_DRM_DW_HDMI_CEC since my kernel is still
>>> missing your patch "drm/meson: dw-hdmi: disable DW-HDMI CEC
>>> sub-driver"). But communication won't work, and dmesg prints timeout
>>> messages:
>>>
>>> [   68.831253] cec-meson_g12a_ao_cec: message ff 84 20 00 06 timed out
>>> [   71.134987] cec-meson_g12a_ao_cec: message ff 87 00 15 82 timed out
>>> [   73.438826] cec-meson_g12a_ao_cec: message f0 timed out
>>> [   75.742677] cec-meson_g12a_ao_cec: message f0 timed out
>>> [   78.046555] cec-meson_g12a_ao_cec: message f0 timed out
>>> [   80.350446] cec-meson_g12a_ao_cec: message f0 timed out
>>> [   82.654358] cec-meson_g12a_ao_cec: message 11 timed out
>>> [   84.958285] cec-meson_g12a_ao_cec: message 11 timed out
>>> [   87.262194] cec-meson_g12a_ao_cec: message 11 timed out
>>> [   89.566130] cec-meson_g12a_ao_cec: message 11 timed out
>>>
>>> I did a quick test with CoreELEC which uses the 4.9 downstream kernel,
>>> CEC seems to work there. So it does not seem to be my hardware setup.
>>>
>>> A quick test with the latest Linux 5.16 shows the same errors.
>>>
>>> Do you happen to have an idea? Do you know if HDMI CEC using upstream
>>> kernels worked at one point on that particular platform?
>>
>> I'm using Arch Linux on my ODROID-n2 (non-plus) and HDMI CEC works as
>> expected.
>> Currently I'm running a 5.15.13-1-aarch64-ARCH kernel. AFAICS the mentioned
>> patch is mainline since v5.14. I can see my TV without issues. I have to add
>> that not every cable is suitable for HDMI CEC, I have one where CEC does not
>> work (in general).
> 
> Hm, interesting, thanks for the datapoint!
> 
> I tried to reproduce your findings, unfortunately I am not successful in
> booting mainline using Arch Linux ARM so far. It seems it comes with
> downstream 4.9 kernel by default (where CEC seems to work in this case
> too). I then installed linux-aarch64 and adjusted the device tree, but
> it seems that the downstream U-Boot 2015.01-10 has some hardcoded
> "rsvmem" command which fails. How are you booting v5.14?

FWIW, adjusted U-Boot load addresses fixed that issue:
# Set load addresses
setenv dtb_loadaddr "0x20000000"
setenv loadaddr "0x1080000"
setenv initrd_loadaddr "0x4080000"

And I can confirm, HDMI CEC works with Arch Linux 5.15.13 kernel!

> 
> It is a bit surprising that 5.15.13 works for you but 5.16 didn't for
> me. That makes me wonder, could it be bootloader dependent? Are you
> using downstream U-Boot?

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.

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.

--
Stefan