Re: [PATCH 1/3] ARM: OMAP2+: 32k-counter: Use hwmod lookup to check presence of 32k timer

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On Friday 30 March 2012 02:02 PM, Hiremath, Vaibhav wrote:
> On Fri, Mar 30, 2012 at 13:11:35, Shilimkar, Santosh wrote:
>> On Fri, Mar 30, 2012 at 12:04 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote:
>>> On Wed, Mar 28, 2012 at 20:19:07, Shilimkar, Santosh wrote:
>>>> On Wed, Mar 28, 2012 at 8:07 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote:
>>>>> On Wed, Mar 28, 2012 at 19:50:02, Shilimkar, Santosh wrote:
>>>>>> On Wed, Mar 28, 2012 at 7:46 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote:
>>>>>>> On Wed, Mar 21, 2012 at 19:30:01, Shilimkar, Santosh wrote:
>>>>>>>> On Wed, Mar 21, 2012 at 5:12 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote:
>>>>>>>>> On Mon, Mar 19, 2012 at 17:45:32, Shilimkar, Santosh wrote:
>>>>>>>>>> On Monday 19 March 2012 05:14 PM, Ming Lei wrote:
>>>>>>>>>>> On Mon, Mar 19, 2012 at 7:11 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote:
>>>>>>
>> [...]
>>
>>>> I thought so and now if you look at last part of my comment.
>>>>
>>>> Rating of 32K based synctimer and 32K based GPTIMER
>>>> should be same because of the precision. That's the main
>>>> point why I was saying that GPTIMER is not a better
>>>> clock-source( with 32k clock src)  than sync timer when
>>>> both are enabled together.
>>>>
>>>
>>> Santosh,
>>>
>>> In case of OMAP, we are using timer 2 for clocksource
>>>
>>> OMAP_SYS_TIMER_INIT(2, 1, OMAP2_CLKEV_SOURCE, 2, OMAP2_MPU_SOURCE)
>>> OMAP_SYS_TIMER_INIT(3, 1, OMAP3_CLKEV_SOURCE, 2, OMAP3_MPU_SOURCE)
>>>
>>> And timer2 as clocksource is never used, since we have CONFIG_OMAP_32K_TIMER
>>> defined in our defconfig.
>>>
>>> Also, after looking at the code, I came across another problem, setup_sched_clock(). But this can be easily fixed, if we source both the timers with same clock (here 32k_fck).
>>>
>>>
>>> Let me propose this,
>>>
>>> How about, if I keep timer2 source always set to 32k_fclk for omap2,3,4?
>>> And also, as mentioned by Santosh, I will register both the clocks as
>>> clocksource with the same rating.
>>> By default, kernel is going to use 32k_counter as a clocksource, and through
>>> Command prompt user can override it without any issues.
>>>
>>> Just to make sure that, whatever I am trying to propse here works and don't get into unknown issue; I changed my code for this, and it is working for me without any issues.
>>
>> Let's not make this more complicated. I guess below simple patch should sort
>> out the issue. I briefly tested it on OMAP4 and it works. let me know
>> if it helps AMxxx machines.
>>
>> Regards
>> Santosh
>>
>> From 0a9283e26174d76ff2753ac88521b61a26b24e8f Mon Sep 17 00:00:00 2001
>> From: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>> Date: Fri, 30 Mar 2012 12:43:29 +0530
>> Subject: [PATCH] ARM: OMAP: Make OMAP clocksource source selection runtime.
>>
>> Current OMAP code support couple of clocksource options based on compilation
>> flag. The 32KHz based sync timer and a gptimer based clock source which can
>> run on 32KHz or system clock (e.g 38.4 MHz). So there can be 3 options.
>>
>> 1. 32KHz synctimer
>> 2. Sysclock based(e.g 38.4 MHz) gptimer
>> 3. 32KHz based gptimer.
>>
>> The optional gptimer based clocksource was added so that it can give the
>> high precision than synctimer so expected usage was 2 and not 3. Unfortunatlly
>> option 2, clocksource doesn't meet the requirement of free-running clock
>> as per clocksource need. It stops in low power states when  sysclock is cut.
>> That makes gptimer based clocksource option useless for OMAP2/3/4 devices
>> with sysclock as a clock input. Option 3 will still work but it is no better'
>> than 32K synctimer based clocksource.
>>
>> So ideally we can kill the gptimer based clocksource option but there are some
>> OMAP based derivative SoCs like AMXXXX which doesn't have synictimer hardware IP
>> and need to fallback on 32KHz based gptimer clocksource.
>>
>> Considering above, make synctimer and gptimer clocksource runtime
>> selectable so that both OMAP and AMXXXX continue to use the same code.
>>
>> Not-yet-signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>> ---
>>  arch/arm/mach-omap2/timer.c |   25 ++++++++-----------------
>>  1 files changed, 8 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
>> index c512bac..3878e59 100644
>> --- a/arch/arm/mach-omap2/timer.c
>> +++ b/arch/arm/mach-omap2/timer.c
>> @@ -234,21 +234,6 @@ static void __init omap2_gp_clockevent_init(int gptimer_id,
>>  }
>>
>>  /* Clocksource code */
>> -
>> -#ifdef CONFIG_OMAP_32K_TIMER
>> -/*
>> - * When 32k-timer is enabled, don't use GPTimer for clocksource
>> - * instead, just leave default clocksource which uses the 32k
>> - * sync counter.  See clocksource setup in plat-omap/counter_32k.c
>> - */
>> -
>> -static void __init omap2_gp_clocksource_init(int unused, const char *dummy)
>> -{
>> -	omap_init_clocksource_32k();
>> -}
>> -
>> -#else
>> -
>>  static struct omap_dm_timer clksrc;
>>
>>  /*
>> @@ -276,7 +261,7 @@ static u32 notrace dmtimer_read_sched_clock(void)
>>  }
>>
>>  /* Setup free-running counter for clocksource */
>> -static void __init omap2_gp_clocksource_init(int gptimer_id,
>> +static void __init omap2_gptimer_clocksource_init(int gptimer_id,
>>  						const char *fck_source)
>>  {
>>  	int res;
>> @@ -295,7 +280,13 @@ static void __init omap2_gp_clocksource_init(int
>> gptimer_id,
>>  		pr_err("Could not register clocksource %s\n",
>>  			clocksource_gpt.name);
>>  }
>> -#endif
>> +
>> +static void __init omap2_gp_clocksource_init(int gptimer_id,
>> +                                                const char *fck_source)
>> +{
>> +	if (omap_init_clocksource_32k())
>> +		omap2_gptimer_clocksource_init(gptimer_id, fck_source);
>> +}
>>
> 
> With this patch, will you be able to choose gptimer as a clocksource
> using bootparameter (or sysfs) for given kernel uImage?
> 
Why do you want that ? Look at changelog. The gptimer based clocksource
is useless for OMAP and for AM devices synctimer is not available.


> The answer is simply NO...as the registration of gptimer is based on
> failure from omap_init_clocksource_32k(). And this is nothing different 
> than my original patch, my patch exactly does same thing.
> 
I ight have missed your original patch. If that patch is similar then
no problems.

> The requirement after 'ming Lie' response on my patch was, there will be
> usecases where we might need to use gptimer for clocksource and with 
> the patch it is not possible, since you will only register 
> 32k_counter here.
> 
I think Ming Lie might have expected that gptimer clocksource might
be better which is not the case.

> So in order to allow user to choose between 32K and gptimer, you must 
> register both and make 32k as a default thing.
> 
As described in the commit log, its not needed at all. Let's not add
a feature which is just useless because the gptimer based clock
source has no advantage against the syntimer.

Hope this clarifies.

Regards
Santosh

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