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From: Giuseppe CAVALLARO on 9 Apr 2010 03:00
Hello!
this function was removed in the past but I've not clear all the details.
While testing LLTng, I wrote the patch, in attachment, that re-adds it
again.
The clocksource_get_next returns the first clock source available
(without looking at the rating).
In my environment, a clock source is a TMU channel (e.g. TMU1) and,
indeed, clocksource_get_next works fine.

Let me know if it makes sense or if I'm missing something.

Best Regards,
Giuseppe
From: john stultz on 9 Apr 2010 17:00
On Thu, Apr 8, 2010 at 11:53 PM, Giuseppe CAVALLARO
<peppe.cavallaro(a)st.com> wrote:
> Hello!
> this function was removed in the past but I've not clear all the details.
> While testing LLTng, I wrote the patch, in attachment, that re-adds it
> again.
> The clocksource_get_next returns the first clock source available
> (without looking at the rating).
> In my environment, a clock source is a TMU channel (e.g. TMU1) and,
> indeed, clocksource_get_next works fine.

Could you provide some more details as to why you need raw access to
the clocksource, instead of using something like ktime_get(),
getrawmonotonic() or sched_clock()?

thanks
-john
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From: Giuseppe CAVALLARO on 12 Apr 2010 02:10
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Hash: SHA1

Hello John,

john stultz wrote:
> On Thu, Apr 8, 2010 at 11:53 PM, Giuseppe CAVALLARO
> <peppe.cavallaro(a)st.com> wrote:
>> Hello!
>> this function was removed in the past but I've not clear all the details.
>> While testing LLTng, I wrote the patch, in attachment, that re-adds it
>> again.
>> The clocksource_get_next returns the first clock source available
>> (without looking at the rating).
>> In my environment, a clock source is a TMU channel (e.g. TMU1) and,
>> indeed, clocksource_get_next works fine.
>
> Could you provide some more details as to why you need raw access to
> the clocksource, instead of using something like ktime_get(),
> getrawmonotonic() or sched_clock()?

I wanted to directly read the value of the TCNT register of a TMU
channel registered as clocksource in an SH platform.
My idea was to get the first clocksource available and than use the read
hook to get its raw value.
Indeed, on SH4, the clocksource_get_next returns the TMU channel 1
(usually registered as clocksource); the clk->reads points to
sh_tmu_clocksource_read (drivers/clocksource/sh_tmu.c). This returns the
value of the timer count register (TCNT).

Best Regards,
Giuseppe

> thanks
> -john

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From: john stultz on 12 Apr 2010 15:00
On Mon, 2010-04-12 at 08:02 +0200, Giuseppe CAVALLARO wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hello John,
>
> john stultz wrote:
> > On Thu, Apr 8, 2010 at 11:53 PM, Giuseppe CAVALLARO
> > <peppe.cavallaro(a)st.com> wrote:
> >> Hello!
> >> this function was removed in the past but I've not clear all the details.
> >> While testing LLTng, I wrote the patch, in attachment, that re-adds it
> >> again.
> >> The clocksource_get_next returns the first clock source available
> >> (without looking at the rating).
> >> In my environment, a clock source is a TMU channel (e.g. TMU1) and,
> >> indeed, clocksource_get_next works fine.
> >
> > Could you provide some more details as to why you need raw access to
> > the clocksource, instead of using something like ktime_get(),
> > getrawmonotonic() or sched_clock()?
>
> I wanted to directly read the value of the TCNT register of a TMU
> channel registered as clocksource in an SH platform.
> My idea was to get the first clocksource available and than use the read
> hook to get its raw value.
> Indeed, on SH4, the clocksource_get_next returns the TMU channel 1
> (usually registered as clocksource); the clk->reads points to
> sh_tmu_clocksource_read (drivers/clocksource/sh_tmu.c). This returns the
> value of the timer count register (TCNT).

If you specifically want the function sh_tmu_clocksource_read(), why not
call it directly instead of indirecting through the clocksource
infrastructure?

Additionally, since the clocksource code is dynamic, you might get a
different clocksource then you expect (such as jiffies) depending on
user config or user actions.

So I'd advise against using the clocksource code here.

thanks
-john




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From: Giuseppe CAVALLARO on 13 Apr 2010 01:50
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 04/12/2010 08:50 PM, john stultz wrote:
> On Mon, 2010-04-12 at 08:02 +0200, Giuseppe CAVALLARO wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Hello John,
>>
>> john stultz wrote:
>>> On Thu, Apr 8, 2010 at 11:53 PM, Giuseppe CAVALLARO
>>> <peppe.cavallaro(a)st.com> wrote:
>>>> Hello!
>>>> this function was removed in the past but I've not clear all the details.
>>>> While testing LLTng, I wrote the patch, in attachment, that re-adds it
>>>> again.
>>>> The clocksource_get_next returns the first clock source available
>>>> (without looking at the rating).
>>>> In my environment, a clock source is a TMU channel (e.g. TMU1) and,
>>>> indeed, clocksource_get_next works fine.
>>>
>>> Could you provide some more details as to why you need raw access to
>>> the clocksource, instead of using something like ktime_get(),
>>> getrawmonotonic() or sched_clock()?
>>
>> I wanted to directly read the value of the TCNT register of a TMU
>> channel registered as clocksource in an SH platform.
>> My idea was to get the first clocksource available and than use the read
>> hook to get its raw value.
>> Indeed, on SH4, the clocksource_get_next returns the TMU channel 1
>> (usually registered as clocksource); the clk->reads points to
>> sh_tmu_clocksource_read (drivers/clocksource/sh_tmu.c). This returns the
>> value of the timer count register (TCNT).
>
> If you specifically want the function sh_tmu_clocksource_read(), why not
> call it directly instead of indirecting through the clocksource
> infrastructure?
>
> Additionally, since the clocksource code is dynamic, you might get a
> different clocksource then you expect (such as jiffies) depending on
> user config or user actions.
>
> So I'd advise against using the clocksource code here.

This means I should export the sh_tmu_clocksource_read (currently
static) and don't pass for the clocksource code at all.

Thanks for your prompt feedback.

Best Regards,
Giuseppe

> thanks
> -john
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