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Date: Tue, 16 Dec 2014 17:05:08 +0530
From: Lokesh Vutla <lokeshvutla@...com>
To: Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
"Kristo, Tero" <t-kristo@...com>, Nishanth Menon <nm@...com>,
Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH 2/2] ARM: omap5/dra7xx: Fix counter frequency drift for
AM572x errata i856.
Hi Lennart,
On Sunday 14 December 2014 10:15 AM, Lennart Sorensen wrote:
> On Fri, Dec 12, 2014 at 05:08:56PM -0500, Lennart Sorensen wrote:
>> Errata i856 for the AM572x (DRA7xx) points out that the 32.768KHz external
>> crystal is not enabled at power up. Instead the CPU falls back to using
>> an emulation for the 32KHz clock which is SYSCLK1/610. SYSCLK1 is usually
>> 20MHz on boards so far (which gives an emulated frequency of 32.786KHz),
>> but can also be 19.2 or 27MHz which result in much larger drift.
>>
>> Since this is used to drive the master counter at 32.768KHz * 375 /
>> 2 = 6.144MHz, the emulated speed for 20MHz is of by 570ppm, or about 43
>> seconds per day, and more than the 500ppm NTP is able to tolerate.
>>
>> Checking the CTRL_CORE_BOOTSTRAP register can determine if the CPU
>> is using the real 32.768KHz crystal or the emulated SYSCLK1/610, and
>> by known that the real counter frequency can be determined and used.
> s/known/knowing/
> and a comma after that.
>> The real speed is then SYSCLK1 / 610 * 375 / 2 or SYSCLK1 * 75 / 244.
Is this applicable for OMAP5 also?
If not can you drop omap5 from $subject?
In order to make the code more simpler, can you use the following logic:
and add documentation accordingly.
diff --git a/arch/arm/mach-omap2/control.h b/arch/arm/mach-omap2/control.h
index a3c0133..a80ac2d 100644
--- a/arch/arm/mach-omap2/control.h
+++ b/arch/arm/mach-omap2/control.h
@@ -286,6 +286,10 @@
#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.
diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
index fb0cb2b..84aadae 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"
@@ -545,6 +546,16 @@ static void __init realtime_counter_init(void)
break;
}
+ if (soc_is_dra7xx()) {
+ reg = omap_ctrl_readl(DRA7_CTRL_CORE_BOOTSTRAP);
+ reg = reg & DRA7_SPEEDSELECT_MASK;
+
+ if (reg) {
+ num = 75;
+ den = 244;
+ }
+ }
+
/* Program numerator and denumerator registers */
reg = readl_relaxed(base + INCREMENTER_NUMERATOR_OFFSET) &
NUMERATOR_DENUMERATOR_MASK;
--
1.9.1
Thanks and regards,
Lokesh
>>
>> Signed-off-by: Len Sorensen <lsorense@...lub.uwaterloo.ca>
>> ---
>> arch/arm/mach-omap2/timer.c | 120 +++++++++++++++++++++++++++++++------------
>> 1 file changed, 87 insertions(+), 33 deletions(-)
>>
>> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
>> index fb0cb2b..f00e4b4 100644
>> --- a/arch/arm/mach-omap2/timer.c
>> +++ b/arch/arm/mach-omap2/timer.c
>> @@ -497,6 +497,7 @@ static void __init realtime_counter_init(void)
>> static struct clk *sys_clk;
>> unsigned long rate;
>> unsigned int reg, num, den;
>> + bool errata_i856_workaround = false;
>>
>> base = ioremap(REALTIME_COUNTER_BASE, SZ_32);
>> if (!base) {
>> @@ -510,39 +511,93 @@ static void __init realtime_counter_init(void)
>> return;
>> }
>>
>> + if (soc_is_dra7xx()) {
>> + #define CTRL_CORE_BOOTSTRAP 0x4A0026C4
>> + #define SPEEDSELECT_MASK 0x00000300
>> + void __iomem *corebase;
>> + corebase = ioremap(CTRL_CORE_BOOTSTRAP, SZ_4);
>> + if (!corebase)
>> + pr_err("%s: ioremap failed\n", __func__);
>> + else {
>> + reg = readl_relaxed(corebase) & SPEEDSELECT_MASK;
>> + iounmap(corebase);
>> + /*
>> + * Errata i856 says the 32.768KHz crystal does
>> + * not start at power on, so the CPU falls back in
>> + * an emulated 32KHz clock instead. This causes
>> + * the master counter frequency to not be 6.144MHz
>> + * This affects at least the AM572x 1.0 and
>> + * 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.
>> + *
>> + * If the two speedselect bits are not 0, then the
>> + * 32.768KHz clock driving the course counter that
> s/course/coarse/
>> + * 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.
>> + */
>> + if (reg) {
>> + errata_i856_workaround = true;
>> + }
>> + }
>> + }
>> +
>> rate = clk_get_rate(sys_clk);
>> - /* Numerator/denumerator values refer TRM Realtime Counter section */
>> - switch (rate) {
>> - case 12000000:
>> - num = 64;
>> - den = 125;
>> - break;
>> - case 13000000:
>> - num = 768;
>> - den = 1625;
>> - break;
>> - case 19200000:
>> - num = 8;
>> - den = 25;
>> - break;
>> - case 20000000:
>> - num = 192;
>> - den = 625;
>> - break;
>> - case 26000000:
>> - num = 384;
>> - den = 1625;
>> - break;
>> - case 27000000:
>> - num = 256;
>> - den = 1125;
>> - break;
>> - case 38400000:
>> - default:
>> - /* Program it for 38.4 MHz */
>> - num = 4;
>> - den = 25;
>> - break;
>> + if (errata_i856_workaround) {
>> + /*
>> + * Realtime Counter frequency is not based on a real
>> + * 32.768KHz time source, so calculate the real resulting
>> + * frequency instead. It is not 6.144MHz in this case.
>> + *
>> + * The frequency is always rate / 610 + 375 / 2 which
>> + * is rate * 244 / 75 and will fit in 32 bit for all rates.
>> + *
>> + * The multiplication has to be first to keep accuracy
>> + * with integer math as high as possible.
>> + */
>> + num = 75;
>> + den = 244;
>> + arch_timer_freq = (rate * num) / den;
>> + } else {
>> + /* Numerator/denumerator values refer TRM Realtime Counter section */
>> + switch (rate) {
>> + case 12000000:
>> + num = 64;
>> + den = 125;
>> + break;
>> + case 13000000:
>> + num = 768;
>> + den = 1625;
>> + break;
>> + case 19200000:
>> + num = 8;
>> + den = 25;
>> + break;
>> + case 20000000:
>> + num = 192;
>> + den = 625;
>> + break;
>> + case 26000000:
>> + num = 384;
>> + den = 1625;
>> + break;
>> + case 27000000:
>> + num = 256;
>> + den = 1125;
>> + break;
>> + case 38400000:
>> + default:
>> + /* Program it for 38.4 MHz */
>> + num = 4;
>> + den = 25;
>> + break;
>> + }
>> + /* This divides cleanly and fits in 32 bits */
>> + arch_timer_freq = (rate / den) * num;
>> }
>>
>> /* Program numerator and denumerator registers */
>> @@ -556,7 +611,6 @@ static void __init realtime_counter_init(void)
>> reg |= den;
>> writel_relaxed(reg, base + INCREMENTER_DENUMERATOR_RELOAD_OFFSET);
>>
>> - arch_timer_freq = (rate / den) * num;
>> set_cntfreq();
>>
>> iounmap(base);
>> --
>> 1.7.10.4
>
> Stupid typos. Will make sure to include in next revision, and maybe
> I can manage to reword the description a bit to make it flow better or
> be clearer.
>
--
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