On 12/16/2014 10:36 AM, Lennart Sorensen wrote:
[...]
>> B) Since rate switch is no longer needed, how about something like the
>> following:
>> diff --git a/arch/arm/mach-omap2/control.h b/arch/arm/mach-omap2/control.h
>> index a3c0133..315d6d1 100644
>> --- a/arch/arm/mach-omap2/control.h
>> +++ b/arch/arm/mach-omap2/control.h
>> @@ -286,6 +286,11 @@
>> #define OMAP5XXX_CONTROL_STATUS 0x134
>> #define OMAP5_DEVICETYPE_MASK (0x7 << 6)
>>
>> +
>> +/* DRA7XX CONTROL CORE BOOTSTRAP */
>> +#define DRA7_CTRL_CORE_BOOTSTRAP 0x6c4
>> +#define DRA7_SPEEDSELECT_MASK (0x3 << 8)
>> +
>> /*
>> * REVISIT: This list of registers is not comprehensive - there are more
>> * that should be added.
>
> I like that as a place for those.
>
>> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
>> index 4f61148..783d3c3 100644
>> --- a/arch/arm/mach-omap2/timer.c
>> +++ b/arch/arm/mach-omap2/timer.c
>> @@ -54,6 +54,7 @@
>>
>> #include "soc.h"
>> #include "common.h"
>> +#include "control.h"
>> #include "powerdomain.h"
>> #include "omap-secure.h"
>>
>
> How about this version for the rest of the file. It handles that for
> the errata case we would like to do rate * num / den, which given how
> small the num is will fit in 32bit and gives the best accuracy for the
> calculation, while the non errata case the existing calculation works
> well and fits in 32 bit for all other cases. It just has to be moved
> up so that the goto can skip it. I changed sysclk to sysclk1 since on
> the dra7xx there is in fact a sysclk1 and a sysclk2 and it is probably
> worth keeping it clear which one this is referring to.
>
> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
> index fb0cb2b..be254bf 100644
> --- a/arch/arm/mach-omap2/timer.c
> +++ b/arch/arm/mach-omap2/timer.c
> @@ -511,6 +511,36 @@ static void __init realtime_counter_init(void)
> }
>
> rate = clk_get_rate(sys_clk);
> +
> + if (soc_is_dra7xx()) {
> + /*
> + * Errata i856 says the 32.768KHz crystal does not start at
> + * power on, so the CPU falls back to an emulated 32KHz clock
> + * based on sysclk1 / 610 instead. This causes the master counter
> + * frequency to not be 6.144MHz but at sysclk1 / 610 * 375 / 2
> + * (OR sysclk1 * 75 / 244)
> + *
> + * This affects at least the DRA7/AM572x 1.0, 1.1 revisions.
> + * Of course any board built without a populated 32.768KHz
> + * crystal would also need this fix even if the CPU is fixed
> + * later.
> + *
> + * Either case can be detected by using the two speedselect bits
> + * If they are not 0, then the 32.768KHz clock driving the
> + * coarse counter that corrects the fine counter every time it
> + * ticks is actually rate/610 rather than 32.768KHz and we
> + * should compensate to avoid the 570ppm (at 20MHz, much worse
> + * at other rates) too fast system time.
> + */
> + reg = omap_ctrl_readl(DRA7_CTRL_CORE_BOOTSTRAP);
> + if (reg & DRA7_SPEEDSELECT_MASK) {
> + num = 75;
> + den = 244;
> + arch_timer_freq = (rate * num) / den;
> + goto sysclk1_based;
> + }
> + }
> +
> /* Numerator/denumerator values refer TRM Realtime Counter section */
> switch (rate) {
> case 12000000:
> @@ -544,7 +574,9 @@ static void __init realtime_counter_init(void)
> den = 25;
> break;
> }
> + arch_timer_freq = (rate / den) * num;
>
> +sysclk1_based:
> /* Program numerator and denumerator registers */
> reg = readl_relaxed(base + INCREMENTER_NUMERATOR_OFFSET) &
> NUMERATOR_DENUMERATOR_MASK;
> @@ -556,7 +588,6 @@ static void __init realtime_counter_init(void)
> reg |= den;
> writel_relaxed(reg, base + INCREMENTER_DENUMERATOR_RELOAD_OFFSET);
>
> - arch_timer_freq = (rate / den) * num;
I see why arch_timer_freq might skip the rounding error of 39, 15 and
55 Vs existing logic which is possibly at a truncation error risk
(without errata for sysclk 13, 26 and 27MHz).
all you'd probably need to do is cast rate, num and den to unsigned
long and have a common computation logic.
if you'd really want to handle truncation error, it must be a separate
patch of it's own - I would not mix it with the errata fix.
--
Regards,
Nishanth Menon
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
