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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Chen,

On 18/06/2015 02:33, Chen Baozi wrote:

> 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?
How did you resolve it on OMAP5432? Does Xen get the timer frequency 
from the property "clock-frequency"?
I'm wondering if we should get the frequency from the OMAP5 specific 
timer register rather than modifying U-boot and/or the DT.
Regards,

--
Julien Grall

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