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Subject: Re: [PATCH 0/4] drm/meson: Module removal fixes
To:     Marc Zyngier <maz@kernel.org>
Cc:     Kevin Hilman <khilman@baylibre.com>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        kernel-team@android.com, dri-devel@lists.freedesktop.org,
        linux-amlogic@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20201116200744.495826-1-maz@kernel.org>
 <0b429c41-421a-2ae0-66a0-a142c56acadd@baylibre.com>
 <09de6683eea499cfd83ab0c67e0cdca2@kernel.org>
From:   Neil Armstrong <narmstrong@baylibre.com>
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Organization: Baylibre
Message-ID: <e73609a6-5502-3a97-d231-c7c419863842@baylibre.com>
Date:   Tue, 17 Nov 2020 10:46:01 +0100
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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