[PATCH v3 06/11] ARM: vexpress: use clocksource_of_init for sp804

[haojian.zhuang@linaro.org (Haojian Zhuang)]

On 13 March 2013 23:19, Pawel Moll <pawel.moll@arm.com> wrote:
> On Wed, 2013-03-13 at 15:01 +0000, Haojian Zhuang wrote:
>> Yes, it's possible. Since only clocksource / clockevent is using SP804 timer
>> on the VE platform. If user app or something else is using other SP804
>> timer, it would be mess because of resource conflict.
>
> How would you expose this device to the app or something else? It's an
> amba_bus device, so it must be bound with an amba_driver. Otherwise
> you're abusing the device model and, well, you're on your own.
>
> The devices are managed by the system. The device tree is merely a
> description of the available hardware.
>
Maybe I didn't express my idea well. My point is that timer could be
clock source
/clock event. It could also just be a timer that user app or other device driver
may want to use it directly. There're a lot of reason that user app or some
 driver wants to use hardware timer. For example, the specific timer may
keep running even system is in low power mode.

Although there's so much hardware timers available, system must choose
one for the usage of clock source / clock event / other hardware timer usage.

>> >> Imagine that only TIMINT1 signal in sp804 is routed to interrupt controller.
>> >> Could system still pick any one it wants?
>> >
>> Then we need another new property. I try to find using minim properties.
>
> No, we don't. See the discussion with Rob. He has an idea (using the
> interrupt property only), I have another one (using already defined
> interrupt-names property). I see you've just came with another one
> (TIMINTC treated as TIMINT1), which is fine with me. Either way you've
> got what you need to make the right decision.
>
After considered as second time, I think that we still need a property to meet
alias usage. Excuse me expand it in this topic.

arm,sp804-has-irq = <offset>;
The offset means TIMER register offset. If it's not zero, TIMER2 is using
irq. And it could be configured as clock event. Otherwise, TIMER1 is clock
event.
We must make sure that only one of all sp804 timers is using this property.

alias:
linux,clocksource = <&sp804-A>
linux,clockevent = <&sp804-A>

Although both of them points to timerA, only TIMER1 or TIMER2 of sp804
is using irq. So one is clock source, and the other is clock event.

alias:
linux,clocksource = <&sp804-A>
linux,clockevent = <&sp804-B>
The issue comes since system don't know whether TIMER1 or TIMER2 could
be configured as clock source.

We still need a new property to claim it. It seems that we can't drop
"arm,sp804-clocksource", although everybody don't like it.

What's your opinion?

>
> Where do you do this? In the Device Tree? No. In the kernel command
> line
Yes, command line could also be filled in DTS.