linux-kernel - Re: next/master bisection: baseline.dmesg.emerg on meson-gxbb-p200

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Date:   Thu, 19 Nov 2020 11:33:06 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Guillaume Tucker <guillaume.tucker@...labora.com>,
        kernelci-results@...ups.io, Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: next/master bisection: baseline.dmesg.emerg on meson-gxbb-p200

On 2020-11-19 10:26, Neil Armstrong wrote:
> On 19/11/2020 11:20, Marc Zyngier wrote:
>> On 2020-11-19 08:50, Guillaume Tucker wrote:
>>> Please see the automated bisection report below about some kernel
>>> errors on meson-gxbb-p200.
>>> 
>>> Reports aren't automatically sent to the public while we're
>>> trialing new bisection features on kernelci.org, however this one
>>> looks valid.
>>> 
>>> The bisection started with next-20201118 but the errors are still
>>> present in next-20201119.  Details for this regression:
>>> 
>>>   https://kernelci.org/test/case/id/5fb6196bfd0127fd68d8d902/
>>> 
>>> The first error is:
>>> 
>>>   [   14.757489] Internal error: synchronous external abort: 96000210
>>> [#1] PREEMPT SMP
>> 
>> Looks like yet another clock ordering setup. I guess different Amlogic
>> platforms have slightly different ordering requirements.
>> 
>> Neil, do you have any idea of which platform requires which ordering?
>> The variability in DT and platforms is pretty difficult to follow (and
>> I don't think I have such board around).
> 
> The requirements should be the same, here the init was done before 
> calling
> dw_hdmi_probe to be sure the clocks and internals resets were 
> deasserted.
> But since you boot from u-boot already enabling these, it's already 
> active.

The crashing platform also boots with u-boot. What is the difference?
No HDMI support?

> The solution would be to revert and do some check in 
> meson_dw_hdmi_init() to
> check if already enabled and do nothing.

It looks more subtle than that, as it also depends on which DT is 
provided
(an early meson_dw_hdmi_init() works with the kernel DT, and breaks with 
the
u-boot DT). So whatever difference is between the two DTs causes havoc.
u-boot obviously only uses its own DT, so we are looking at a kernel bug 
here.

Not having this patch also breaks module reinsertion (HDMI clocks are 
disabled
on unbind), so *something* has to be done late.

So here are my questions:
- What breaks in my config when I boot using u-boot's DT?
- How to detect early that the registers are clocked or not?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...