Re: [PATCH] clocksource: SuperH TMU Timer driver

[Shin-ichiro KAWASAKI <kawasaki@juno.dti.ne.jp>]

Paul Mundt wrote:
> On Mon, Jun 01, 2009 at 07:50:40PM +0900, Magnus Damm wrote:
>> 2009/5/30 Shin-ichiro KAWASAKI <kawasaki@juno.dti.ne.jp>:
>>> I made some investigation, and found that the warnings are printed
>>> after zero value is set to TCOR. ?I checked SH7785 hardware manual,
>>> but could not find any description what happens when zero value set
>>> to TCOR.
>> Thanks for investigating. I read a few SH manuals before converting
>> the old driver, but I couldn't find any description of zero value.
>> Same as you.
>>
>> The idea with zero value TCOR comes from the old driver. It may be
>> there for some historical reason, or it may just be plain wrong. I've
>> sometimes seen interrupt bursts with the old tmu driver which may be
>> related.
>>
> It was mostly there just because it worked and seemed like a reasonable
> thing to do, and because no one had any better ideas on what to do in
> that situation. But yes, technically the behaviour is undefined, and so
> finding something slightly more precise is a good idea.

Thank you for your explanations, Magnus, Paul!
It has got clearer for me.

I guess there are two solutions.

 i)  Add one-shot timer feature to qemu-sh's TMU emulation.
     (Even though this feature is not documented.)
 ii) Modify sh-linux TMU driver not to set zero value to TCOR.
     (A status will be added to sh_tmu_priv.)

I'll consider on both of them, but that will take a week or so.
Any help from others will be appreciated.


Regards,
Shin-ichiro KAWASAKI