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

[Tim Deegan <tim@xxxxxxx>]

At 09:05 +0900 on 26 Jun (1372237555), Sengul Thomas wrote:
> >
> > Timers on ARM seems a bit complex. The current issue is with arch timer
> > (which is also used by dom0).
> 
> Just out of curiosity, what is the difference between arch timer and
> platform timer?

The arch timer has its interface specified in the CPU manual and
required (IIRC) for any processor that supports the virt extensions.
The platform timers are whatever other time sources come on the SoC
you're running on.

Having thought about this a bit, ISTR that the register in Julien's
patch doesn't control anything -- it's there to tell the arch timer's
users how fast that timer is going, so it ought to be set up by whatever
sets up the timer itself (turning on oscillators &c).

So the right thing to do is to move that write into more board-specific
start-of-day code (and eventually into the boot-wrapper), and rely on
the bootloader/firmware to have done it in the general case.  On a real
TC2 is that register already correct at (xen's) boot time?

But presumably just changing it from 100KHz to 24KHz for all vexpresses
is wrong because that will break things on the software models in the
opposite way.

Tim.

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