Re: [Xen-devel] [PATCH 3/4] xen: set the right flags when enabling interrupts for 8250

[Chen Baozi <baozich@xxxxxxxxx>]

On Jul 25, 2013, at 8:33 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:

> On 07/25/2013 12:31 PM, Chen Baozi wrote:
>> 
>> On Jul 25, 2013, at 7:17 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>> 
>>> On 07/25/2013 10:14 AM, Chen Baozi wrote:
>>> 
>>>> Besides this test, I noticed that we set a timer to poll UART after 
>>>> enabling
>>>> the interrupt. And the timer initialization codes are platform specific, 
>>>> which
>>>> should be implemented in xen/arch/arm/platforms/omap5.c for example. 
>>>> However,
>>>> I haven't done this yet. (I used to plan to turn to this work after UART 
>>>> porting
>>>> has been done.) Is it a possible factor that may cause my issues?
>>> 
>>> Xen uses the arch timers to handle the time. On some platform (for
>>> instance the Arndale), it's not enabled by default.
>>> 
>>> If the omap5 boot with the arch timers enabled, you don't need to
>>> implement the init_time callback.
>>> 
>>> Do you know if Xen receives timer interrupts?
>> 
>> Any way that I could confirm this?
>> 
>> There is a line of boot message:
>> 
>> "Using generic timer at 0 KHz."
>> 
> 
> It seems the arch timer is not configured/enabled. Do you know if U-boot
> enables it?

I could see clocks.c/clocks.o in its u-boot sources, but I don't think U-boot 
has already enabled it, for I could read such lines from Linux kernel boot 
messages:

"""
OMAP clockevent source: GPTIMER1 at 32768 Hz
sched_clock: 32 bits at 32kHz, resolution 30517ns, wraps every 131071999s
OMAP clocksource: 32k_counter at 32768 Hz
arch_timer: No interrupt available, giving up
omap5_realtime_timer_init: arch_timer_register failed -22

> 
> It's not clear to me, how you need to implement init_time. Do you have a
> datasheet with the board? If yes, is there a section for the section timer?

Yes, TI has published an 49.6MB Technical Reference Manual online with 88 pages 
section about timer.

> 
> Perhaps the good start is linux/arch/arm/mach-omap2/timer.c.

Thanks a lot, it should be helpful!

Baozi


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