On 17/11/2020 10:19, Marc Zyngier wrote:
> Hi Neil,
>
> On 2020-11-17 08:49, Neil Armstrong wrote:
>> Hi Marc,
>>
>> On 16/11/2020 21:07, Marc Zyngier wrote:
>>> Hi all,
>>>
>>> Having recently moved over to a top-of-the-tree u-boot on one of my
>>> VIM3L systems in order to benefit from unrelated improvements
>>> (automatic PCIe detection, EFI...), I faced the issue that my kernel
>>> would hang like this:
>>>
>>> [ OK ] Finished Helper to synchronize boot up for ifupdown.
>>> [ OK ] Started Rule-based Manager for Device Events and Files.
>>> [ 7.114516] VDDCPU: supplied by regulator-dummy
>>> [ OK ] Found device /dev/ttyAML0.
>>> [ 7.146862] meson-drm ff900000.vpu: Queued 2 outputs on vpu
>>> [ 7.169630] fb0: switching to meson-drm-fb from simple
>>> [ 7.169944] Console: switching to colour dummy device 80x25
>>> [ 7.179250] meson-drm ff900000.vpu: CVBS Output connector not available
>>>
>>> and that's it.
>>>
>>> After some poking around, I figured out that it is in the
>>> meson-dw-hdmi module that the CPU was hanging...
>>
>> I'll be interested in having your kernel config, I never had such report
>> since I enabled HDMI support in U-Boot a few years ago.
>
> Yeah, I was pretty surprised too. I have a hunch that this is caused
> by u-boot DT exposing an extra MMIO region (dubbed "hhi") that gets
> picked up by the kernel driver. *Not* having the region in the DT
> (as in the kernel's version of the same DT) makes the driver work
> exactly once:
Yeah, we used this to simplify our u-boot driver, the bindings were missing this
memory space, it should be fixed at some point and stop relying on the
main drm driver to get this memory space.
>
> Decompiled u-boot DT:
>
> hdmi-tx@0 {
> compatible = "amlogic,meson-g12a-dw-hdmi";
> reg = <0x00 0x00 0x00 0x10000 0x00 0x3c000 0x00 0x1000>;
> [...]
> reg-names = "hdmitx\0hhi";
>
> Decompiled kernel DT:
>
> hdmi-tx@0 {
> compatible = "amlogic,meson-g12a-dw-hdmi";
> reg = <0x00 0x00 0x00 0x10000>;
>
> There seem to be some complex interactions between the HDMI driver
> and the DRM driver, both using this MMIO region at any given time.
> But I admit not having tried very hard to follow the DRM maze of
> intricate callbacks. All I needed was this box to reliably boot with
> the firmware-provided DT.
Yes, the HDMI stuff has some dependencies on the DRM display subsystem.
I plan to reorganize stuff but I lack time...
Anyway, thanks.
Applying to drm-misc-next
Neil
>
> You can find a reasonably recent version of my config at [1].
>
> M.
>
> [1] http://www.loen.fr/tmp/Config.full-arm64
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