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

[Brandon Perez <a0225893@xxxxxx>]

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 prevented the kernel from ever getting to boot because the 
SCHEDULE SOFTIRQ was never getting a chance to run, because there would 
always be a timer SOFTIRQ taking precedence over it.
   This has resolved the issue, at least for Xen.

Brandon

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