Re: [PATCH] ARM: dts: Update arch timer node with clock frequency

[Olof Johansson <olof@lixom.net>]

On Wed, Oct 9, 2013 at 1:25 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Tue, Oct 08, 2013 at 11:15:47PM +0100, Olof Johansson wrote:
>> [Adding Tony, who reported a mainline booting issue, and Sean who
>> helped me track this down]
>>
>> On Mon, Sep 23, 2013 at 7:15 AM, Mark Rutland <mark.rutland@arm.com> wrote:
>> > On Sat, Sep 21, 2013 at 04:24:59PM +0100, Tomasz Figa wrote:
>> >> Hi Yuvaraj,
>> >>
>> >> On Wednesday 18 of September 2013 15:41:53 Yuvaraj Kumar C D wrote:
>> >> > Without the "clock-frequency" property in arch timer node, could able
>> >> > to see the below crash dump.
>> >> [snip]
>> >> > diff --git a/arch/arm/boot/dts/exynos5250.dtsi
>> >> > b/arch/arm/boot/dts/exynos5250.dtsi index 7d7cc77..668ce5d 100644
>> >> > --- a/arch/arm/boot/dts/exynos5250.dtsi
>> >> > +++ b/arch/arm/boot/dts/exynos5250.dtsi
>> >> > @@ -96,6 +96,7 @@
>> >> >                          <1 14 0xf08>,
>> >> >                          <1 11 0xf08>,
>> >> >                          <1 10 0xf08>;
>> >> > +           clock-frequency = <24000000>;
>> >>
>> >> Shouldn't it rather come from some clock provided by some clock controller
>> >> instead?
>> >>
>> >> The frequency would be then retrieved using clk_get_rate() on a clock
>> >> received by clk_get(), specified in device tree using generic clock
>> >> bindings.
>> >
>> > If the bootloader has initialised the generic timer correctly, the
>> > CNTFRQ register should contain the clock frequency, independent of any
>> > external clock.
>>
>> So, we just sat here to bisect a problem on the Samsung Chromebook
>> where we hit exactly this problem. The read-only firmware on the
>> device does not set CNTFRQ at boot, so this fails.
>
> Ouch. That's a shame.
>
> A chained bootloader (like the KVM guys are using) should be able to set
> CNTFRQ, so as long as any chained loader actually does that this won't
> cause that to blow up...

Yes, but we have cases where we want to be able to boot without a
chained u-boot as well.

>> Apparantly the u-boot that comes with Arndale sets it, so I haven't
>> seen this error on that platform.
>>
>> > Having the bootloader set CNTFRQ is by far the preferable solution, it
>> > is architected for this purpose.
>>
>> Unfortunately there is now real hardware out there that needs this due
>> to firmware bugs / missing features, so there's little other choice.
>> :(
>
> Indeed :(
>
>>
>> I'll pick this patch up in the fixes branch for 3.12, unless someone
>> complains loudly.
>
> Could you please add a note to the dts regarding why we actually need
> this? It would be nice to maintain the impression that this is not the
> preferred way of doing things...

s/dts/dtsi/, yes I can do that. Hopefully with that we won't get too
much automated copy and paste to other platforms.

It looks like current upstream u-boot got the timer enablement patches
merged together with HYP support, which explains why I didn't see this
on Arndale since it has a forked version of u-boot from Linaro
somewhere.


-Olof