[PATCH v2 05/14] ARM: integrator: use clocksource_of_init for sp804

[Haojian Zhuang]

On 13 March 2013 04:52, Rob Herring <robherring2 at gmail.com> wrote:
> On 03/12/2013 02:33 PM, Arnd Bergmann wrote:
>> On Tuesday 12 March 2013, Rob Herring wrote:
>>> On 03/12/2013 12:08 PM, Haojian Zhuang wrote:
>
> Since the primecell ID registers are defined to be at 0xFF? offset, it
> is quite impossible for the integrator timers to have the ID registers
> within their 0x100 address space.
>
I'm sorry that I don't know this. I can add "arm,integrator-timer" into
compatible table of sp804 driver. I think that we could resolve this
issue. What's your opinion?

>>
>>>>     };
>>>>
>>>>     timer1: timer at 13000100 {
>>>> -           compatible = "arm,integrator-timer";
>>>> +           compatible = "arm,sp804", "arm,primecell";
>>>> +           arm,sp804-clockevent = <0>;
>>>
>>> I don't like this nor the old way with aliases. We should describe the
>>> h/w features of the timer to determine what to use it for. AFAICT, all 3
>>> timers are identical on integrator and it does not matter which one
>>> Linux picks for clocksource vs. clockevent.
>>
>> Interesting point. I remember we had a discussion about this when the
>> initial binding integrator code was merged, but I don't remember what
>> the intent was for doing it like this. Probably just minimizing the
>> changes to the existing code.
>
> Re-reading the thread on this for Integrator, I don't think any
> conclusion was really made, but it got merged. I don't think we should
> a) change the existing alias names or b) expand their usage. OMAP is a
> good example of lots of timers and using h/w properties to select
> particular instances based on properties. I think on the ARM boards the
> selection has been pretty arbitrary. I traced the commit history back
> for the timer code and could not find any evidence to the contrary
> except on VExpress which has broken sp804 on the core tile.
>
> Another part is sched_clock selection. I use the sp804 on highbank, but
> the ARM boards have their 24MHz counter. Also, if I'm on midway, then I
> want to use the arch timers even though the sp804 is still there. My
> sched_clock patches yesterday attempt to address that. Any comments on
> what characteristics should be used to select timer would be helpful.
> Higher frequency and/or bits is better, but to what limit in frequency?
>
> Rob
>