Re: [PATCH 00/10] omap init_early changes for irq and timer init

From: Santosh Shilimkar <santosh.shilimkar@ti.com>
To: Tony Lindgren <tony@atomide.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org
Subject: Re: [PATCH 00/10] omap init_early changes for irq and timer init
Date: Thu, 31 Mar 2011 13:46:49 +0530	[thread overview]
Message-ID: <4D943871.4030206@ti.com> (raw)
In-Reply-To: <20110330182211.GE18334@atomide.com>

On 3/30/2011 11:52 PM, Tony Lindgren wrote:
> * Santosh Shilimkar<santosh.shilimkar@ti.com>  [110330 00:53]:
>>
>> After going through entire series again, it looks very
>> good clean-up and right step towards moving rest of
>> the timer to drivers/ directory.
>>
>> I also realized that the discussion we had before this series was
>> because of miss-understating about the 'wakeu_up' timer
>> terminology. After this series I see that you were mentioning
>> about the pm debug timer where as I was taling about
>> clock-event wakeups from CPUidle point of view.
>
> Well this patcheset keeps the current behaviour, except for
> the PM debug hack to program gpt1.
>
This is the problem what I see.

> What it does not have is the code to dedicate gpt1 for PM
> code, which can be done later once all the other dmtimer
> changes are done.
>
Which not possible to do unless you plan to hack generic
timer framework or waste additional timer hardware for
this.

> So the earlier discussion is still a separate issue from the
> PM debug hack removed in this series. I'll post some patches
> later on for that.
>
No that discussion become relevant with this series now.

>> I still have few concerns about this series.
>>
>> 1)We have removed the flexibility if choosing the timer from
>>    from board files and hard-coded them in platform timer
>>    header.
>
> Well it's not removed, you can still select the timer setup
> by setting .timer entry in the board-*.c file.
>
> So for example, we have omap3_timer and omap3_beagle_timer
> for the beagle rev a&  b based boards.
>
This is exactly my point. This is the board specific data which
is now getting moved to generic headers.

>>   Below board related hard-coding in platform files looks more
>>   hacky and the interface done  by Pual still has a merits of
>>   its own.
>>
>> --- a/arch/arm/plat-omap/include/plat/common.h
>> +++ b/arch/arm/plat-omap/include/plat/common.h
>> @@ -34,7 +34,12 @@
>>   struct sys_timer;
>>
>>   extern void omap_map_common_io(void);
>> -extern struct sys_timer omap_timer;
>> +extern struct sys_timer omap1_timer;
>> +extern struct sys_timer omap242x_timer;
>> +extern struct sys_timer omap243x_timer;
>> +extern struct sys_timer omap3_timer;
>> +extern struct sys_timer omap3_beagle_timer;
>> +extern struct sys_timer omap4_timer;
>>   extern bool omap_32k_timer_init(void);
>>   extern int __init omap_init_clocksource_32k(void);
>>   extern unsigned long long notrace omap_32k_sched_clock(void);
>
> Hmm the only reason for omap3_beagle_timer naming is the
> hardware bug in rev a&  b beagle boards.
>
>> +/*
>> + * Beagle based designs typically have an issue with gptimer1. Also note
>> + * that GPTIMER12 can only use the secure 32KiHz clock source.
>> + */
>>   static void __init omap3_beagle_timer_init(void)
>>   {
>>   	omap_dm_timer_init();
>> -	omap2_gp_clockevent_init();
>> +	omap2_gp_clockevent_init(OMAP3_BEAGLE_TIMER, OMAP3_CLKEV_SOURCE);
>>   	omap2_gp_clocksource_init();
>>   }
>
> Got any better name in mind for that timer?
>
> For removing the old interface, I don't see any reason to
> select timer combinations on omap3 other than omap3_timer
> and omap3_beagle_timer.
>
> If there's need, any new valid sane combinations can be esily
> added, although I seriously doubt that we'll need more for
> omap3.
>
May be I am wrong but the point is about the merit of the
solution even if there are only couple of board files where
we use that interface.

It much cleaner and simpler to say timerid=X, from board
file rather than creating a "struct sys_timer" instance
and putting that in timer code.

>> 2) In patch [6/10], you have removed wakeup timer debug
>> capability with comment "Later on we can reserve gptimer1
>> for PM code only and have similar functionality".
>>
>> I don't know how this will work on OMAP. GPTIMER1 is the
>> only timer which is in always on power domain and wakeup
>> OMAP from deeper power states like CORE OSWR, CORE OFF,
>> DEVICE OFF.
>
> Right, that's why the PM code should manage it for the wake-up
> events. For the clockevent and clocksource we just want to
> use something fast for the runtime.
>
> Then when we hit idle, we can just let PM code program gpt1
> for the wake-up event.
>
>> We do implement these C-state in CPUidle as well and hence
>> the clock-event is expected to be of wakeup-capable.
>> Hence GPTIMER1 is already reserved for clock-event.
>
> The PM code can easily deal with gpt1 by either calling
> next_timer_interrupt, or just by cloning the clockevent
> timer value. But again, that's a separate patch series
> to come..
>
>> The wakeup timer used was only in suspend scenario's
>> and that point of time the timer system is already
>> suspended. So during that even if TIMER1 is re-used
>> for wakeup (which is the case), I don't see any issue.
>
> The reason is that for performance and latency reasons
> we want to use localtimers for runtime on omap4+, and
> need only gpt1 for PM wake-up.
>
This is already the case with or without this series.
> The gpt1 using 32KiHz source clock is a very slow clock
> to reprogram as it's on the external bus.
>
Even its slow, to make CPUIDLE work in low power modes and
you need this clock-event as well. This is where the
generic timer framework with C3STOP helps.

>> At least I don't see other solution than using GPT1
>> for wakeup.
>
> Right, there's no other way to wake except gpt1 or wake-up
> enabled gpio lines. But we don't need to use gpt1 during
> runtime at all.
>
This is not entirely correct and I think this is the point
where we are not on same page. During runtime, gpt1 clock
event is not used for tick generation but it's kept
programmed because low power state switch via
get triggered any time and on any CPU.

This is the same problem as X86 APIC timer + HPET
switching and I worked with Thomas G and Russell
to get this working on ARM platforms using generic
timer framework. No hacking is needed in PM code
for this.

>> 3) You have created few functions so that they can
>> be used between system timer and dmtimer driver code.
>> When we move the dmtimer driver to say some drivers/
>> directory. Is it allowed to share such functions from
>> device drivers
>
> The only function we for clockevent and clocksource is
> the init_one function, which will be implemented in in
> arch/arm/mach-omap2/timer.c anyways. The function to
> reprogram the timer is an inline function so dmtimer
> can then be a loadable driver module :)
>
Great. This was more of question for my undertanding.

For me, with current set of patches, suspend wakeup using
GPT1 is not possible.
It's not a big problem because it's just debug aid and
production kernel doesn't use this as such.

Regards
Santosh