Re: [PATCH] xen/arm: Propagate clock-frequency to DOMU if present in the DT timer node

[Julien Grall <julien.grall@citrix.com>]

On 05/06/2015 21:14, Chris (Christopher) Brand wrote:
> Hi Julien,

Hi Chris,

>> When the property "clock-frequency" is present in the DT timer node, it means that the bootloader/firmware didn't correctly configured the
> CNTFRQ/CNTFRQ_EL0 on each processor.
>
> I did try this out, and it didn't affect my results. I don't understand why, though :-)

My test was limited as I don't have a platform where CNTFRQ/CNTFRQ_EL0 
is not valid. I may have done a mistake in the code.

> What I see is that in preinit_xen_time(), the call to dt_property_read_u32() returns zero. When I built Xen, I set CONFIG_DTB_FILE, and looking at the corresponding dts file it has a timer node with a clock-frequency property. I know that our bootloader also creates a DTB, though, and it looks like that one does *not* have a clock-frequency property in the timer node, so I guess Xen ends up using that one somehow. CNTFRQ on core 0 (only) is also set to the correct frequency, so I end up with the correct frequency in my Dom0 kernel anyway.

dt_property_read_u32 returns 0 when it cannot find a property or because 
the size of the value is not valid.

The device tree provided via CONFIG_DTB_FILE will always take precedence 
to the one pass by the bootloader.

How do you set CONFIG_DTB_FILE?

I would also look to see if by any chance the wrong device tree is set 
via CONFIG_DTB_FILE.

You can check what is the device tree used by dumping it from DOM0. 
Thought, it may be slightly different (some nodes are rewritten). You 
can dump it using dtc -I fs /proc/device-tree -O dts

Regards,

[1] 
http://wiki.xen.org/wiki/Xen_ARM_with_Virtualization_Extensions/Multiboot

-- 
Julien Grall