Re: [Xen-users] [Xen-Users] Issues Booting Dom0 on ARM Cortex A15

[Chen Baozi <cbz@xxxxxxxxxx>]

Hi Brandon,

On Wed, Jun 17, 2015 at 04:00:38PM -0400, Brandon Perez wrote:
> On 06/17/2015 03:15 PM, Julien Grall wrote:
> >Hello Brandon,
> >
> >On 17/06/2015 15:30, Brandon Perez wrote:
> >>The console and keyhandler are receiving 'q' and '0', but nothing is
> >>happening/being printed out. I suspect this is because they are
> >>scheduled as tasklets, and are never getting a chance to run.
> >>
> >>Opening the debugger, it seems like I'm stuck doing timer softirqs and
> >>handling timer interrupts continually. I'm going to double check the
> >>timer settings in my device tree.
> >
> >Looking to your first log [1], it seems that CNTFRQ is not set correctly:
> >
> >Generic Timer IRQ: phys=30 hyp=26 virt=27 Freq: 0 KHz
> >
> >The CNTFRQ register should be set by the firmware/bootloader. Does the
> >Linux kernel is booting on baremetal with the same firmware/bootloader?
> >
> >If yes, do you use the same device tree?
> >
> >Regards,
> >
> 
> Hi Julien,
> 
>     Good catch! That seems to have been the issue. To answer your questions,
> yes the kernel is booting with same firmware, bootloader, and device tree as
> Xen.
> 
>     The real issue actually stems from the uBoot code, which was not
> properly setting the CNTFRQ register (which was indeed 0).
> 
>     The CNTFRQ register being 0 lead to a whole slew of issues, the primary
> of which being was that the timer interrupt ran extremely often, causing
> progress in preemptable sections of code to be extremely slow.

This reminds me that I have had a similar issue when doing OMAP5432 enablement.
IIRC, OMAP5 uses a different platform register for system timer, and CNTFRQ
is not actually used during platform initialisation in linux kernel. Maybe
it would be a good idea to have a check whether your SoC has the same
implementation?

Cheers,

Baozi.

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