Re: [Xen-devel] [PATCH] xen/arm: Set up Versatile Express timer frequency to 24 Mhz

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 24 Jun 2013, Tim Deegan wrote:
> At 14:10 +0100 on 24 Jun (1372083058), Julien Grall wrote:
> > On TC2, the timer frequency was set to 100 Mhz which slows down the whole
> > platform.
> > When Linux is running on bare metal, the frequency is 24 Mhz.
> > 
> > "sleep 60" in dom0 takes:
> >   - 4 mins with a frequency equals to 100 Mhz
> >   - 1 min with a frequency equals to 24 Mhz
> > 
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> Is this a problem with the vexpress (e.g. the timer runs at 24MHz
> regardless of this setting, which would explain the otherwise odd
> numbers you give above), or just that linux code assumes the timer is
> always 24MHz?
> 
> If it's the latter, I think it needs to be fixed on the linux side.  Xen
> can't let the guest OS dictate things like this, since we might want to
> run two guests with different OSes.  Also, if linux changes its choice,
> we'd have trouble with old and new linux running together.

Linux gets the frequency from:

1) device tree
2) the arch timer register

in this order.
Either way it should work.

Could it be that Xen is failing to set the frequency on the versatile
express? Therefore the hardware is running the timer at a different
frequency than Xen is expecting it to?

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