Re: Peach Pi/Pit boot failures in linux-next (was Re: [RFC PATCH 1/1] drm/exynos: Move platform drivers registration to module init)

[Javier Martinez Canillas <javier.martinez@collabora.co.uk>]

[adding Tushar Behera and Doug Anderson to cc list]

Hello,

On 11/24/2014 12:12 PM, Krzysztof Kozlowski wrote:
> On pon, 2014-11-24 at 12:07 +0100, Javier Martinez Canillas wrote:
>> Hello Krzysztof,
>> 
>> > It seems that mau_epll has to be enabled... or something is wrong with
>> > clock hierarchy.
>> >
>> 
>> Another strange thing is that the problem does not happen for some people
>> using the same board, kernel and config options. For example Vivek and Ajay
>> report that they can't reproduce the issue on a Peach Pi using next-20141121
>> and exynos_defconfig without using clk_ignore_unused.
> 
> Maybe they have different bootloader which messes here by enabling some
> clock?
> 
> Anyway it is reproducible on at least some Arndale Octa (Kevin's and
> mine) and Peach Pi boards (yours).
> 

This issue started to look extremely familiar to me so I searched in
my mail inbox and found that the same problem was previously reported
by Kevin a couple of months ago [0] and Tushar provided a fix [1].

I tested linux-next + [1] and that indeed fixes the hang on Peach.

To save you a click, the problem as explained by Tushar is that the
AUDSS mux has two parents: XXTI crystal and MAU_EPLL clock. But when
the output of AUDSS mux is gated, no operations can be made on the
clocks provided by MAU block. For some reason the kernel just oops
so it seems to be a H/W errata?

Mike was not fond about the solution proposed in [1] but something
along those lines would be needed maybe Tushar can comment on that.

Vivek and Ajay,

As explained in [0], you are not facing this issue because your RW
U-Boot seems to predate when audio support was enabled by default.

Can you try executing "sound init" in the U-Boot prompt and see if
that triggers the hang for you?

Best regards,
Javier

[0]: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/262259.html
[1]: http://www.spinics.net/lists/arm-kernel/msg337970.html