ARM: OMAP3+: Implement timer workaround for errata i103 and i767

Errata Titles:
i103: Delay needed to read some GP timer, WD timer and sync timer
      registers after wakeup (OMAP3/4)
i767: Delay needed to read some GP timer registers after wakeup (OMAP5)

Description (i103/i767):
If a General Purpose Timer (GPTimer) is in posted mode
(TSICR [2].POSTED=1), due to internal resynchronizations, values read in
TCRR, TCAR1 and TCAR2 registers right after the timer interface clock
(L4) goes from stopped to active may not return the expected values. The
most common event leading to this situation occurs upon wake up from
idle.

GPTimer non-posted synchronization mode is not impacted by this
limitation.

Workarounds:
1). Disable posted mode
2). Use static dependency between timer clock domain and MPUSS clock
    domain
3). Use no-idle mode when the timer is active

Workarounds #2 and #3 are not pratical from a power standpoint and so
workaround #1 has been implemented. Disabling posted mode adds some CPU
overhead for configuring and reading the timers as the CPU has to wait
for accesses to be re-synchronised within the timer. However, disabling
posted mode guarantees correct operation.

Please note that it is safe to use posted mode for timers if the counter
(TCRR) and capture (TCARx) registers will never be read. An example of
this is the clock-event system timer. This is used by the kernel to
schedule events however, the timers counter is never read and capture
registers are not used. Given that the kernel configures this timer
often yet never reads the counter register it is safe to enable posted
mode in this case. Hence, for the timer used for kernel clock-events,
posted mode is enabled by overriding the errata for devices that are
impacted by this defect.

For drivers using the timers that do not read the counter or capture
registers and wish to use posted mode, can override the errata and
enable posted mode by making the following function calls.

	__omap_dm_timer_override_errata(timer, OMAP_TIMER_ERRATA_I103_I767);
	__omap_dm_timer_enable_posted(timer);

Both dmtimers and watchdogs are impacted by this defect this patch only
implements the workaround for the dmtimer. Currently the watchdog driver
does not read the counter register and so no workaround is necessary.

Posted mode will be disabled for all OMAP2+ devices (including AM33xx)
using a GP timer as a clock-source timer to guarantee correct operation.
This is not necessary for OMAP24xx devices but the default clock-source
timer for OMAP24xx devices is the 32k-sync timer and not the GP timer
and so should not have any impact. This should be re-visited for future
devices if this errata is fixed.

Confirmed with Vaibhav Hiremath that this bug also impacts AM33xx
devices.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

1 files changed, 41 insertions, 8 deletions

diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
index a135d28e202c..63229c5287e6 100644
--- a/arch/arm/mach-omap2/timer.c
+++ b/arch/arm/mach-omap2/timer.c
@@ -222,10 +222,24 @@ void __init omap_dmtimer_init(void)
 	}
 }
 
+/**
+ * omap_dm_timer_get_errata - get errata flags for a timer
+ *
+ * Get the timer errata flags that are specific to the OMAP device being used.
+ */
+u32 __init omap_dm_timer_get_errata(void)
+{
+	if (cpu_is_omap24xx())
+		return 0;
+
+	return OMAP_TIMER_ERRATA_I103_I767;
+}
+
 static int __init omap_dm_timer_init_one(struct omap_dm_timer *timer,
 						int gptimer_id,
 						const char *fck_source,
-						const char *property)
+						const char *property,
+						int posted)
 {
 	char name[10]; /* 10 = sizeof("gptXX_Xck0") */
 	const char *oh_name;
@@ -311,10 +325,15 @@ static int __init omap_dm_timer_init_one(struct omap_dm_timer *timer,
 	}
 	__omap_dm_timer_init_regs(timer);
 	__omap_dm_timer_reset(timer, 1, 1);
-	timer->posted = 1;
 
-	timer->rate = clk_get_rate(timer->fclk);
+	if (posted)
+		__omap_dm_timer_enable_posted(timer);
+
+	/* Check that the intended posted configuration matches the actual */
+	if (posted != timer->posted)
+		return -EINVAL;
 
+	timer->rate = clk_get_rate(timer->fclk);
 	timer->reserved = 1;
 
 	return res;
@@ -326,7 +345,17 @@ static void __init omap2_gp_clockevent_init(int gptimer_id,
 {
 	int res;
 
-	res = omap_dm_timer_init_one(&clkev, gptimer_id, fck_source, property);
+	clkev.errata = omap_dm_timer_get_errata();
+
+	/*
+	 * For clock-event timers we never read the timer counter and
+	 * so we are not impacted by errata i103 and i767. Therefore,
+	 * we can safely ignore this errata for clock-event timers.
+	 */
+	__omap_dm_timer_override_errata(&clkev, OMAP_TIMER_ERRATA_I103_I767);
+
+	res = omap_dm_timer_init_one(&clkev, gptimer_id, fck_source, property,
+				     OMAP_TIMER_POSTED);
 	BUG_ON(res);
 
 	omap2_gp_timer_irq.dev_id = &clkev;
@@ -360,7 +389,7 @@ static bool use_gptimer_clksrc;
 static cycle_t clocksource_read_cycles(struct clocksource *cs)
 {
 	return (cycle_t)__omap_dm_timer_read_counter(&clksrc,
-						     OMAP_TIMER_POSTED);
+						     OMAP_TIMER_NONPOSTED);
 }
 
 static struct clocksource clocksource_gpt = {
@@ -375,7 +404,7 @@ static u32 notrace dmtimer_read_sched_clock(void)
 {
 	if (clksrc.reserved)
 		return __omap_dm_timer_read_counter(&clksrc,
-						    OMAP_TIMER_POSTED);
+						    OMAP_TIMER_NONPOSTED);
 
 	return 0;
 }
@@ -453,12 +482,15 @@ static void __init omap2_gptimer_clocksource_init(int gptimer_id,
 {
 	int res;
 
-	res = omap_dm_timer_init_one(&clksrc, gptimer_id, fck_source, NULL);
+	clksrc.errata = omap_dm_timer_get_errata();
+
+	res = omap_dm_timer_init_one(&clksrc, gptimer_id, fck_source, NULL,
+				     OMAP_TIMER_NONPOSTED);
 	BUG_ON(res);
 
 	__omap_dm_timer_load_start(&clksrc,
 				   OMAP_TIMER_CTRL_ST | OMAP_TIMER_CTRL_AR, 0,
-				   OMAP_TIMER_POSTED);
+				   OMAP_TIMER_NONPOSTED);
 	setup_sched_clock(dmtimer_read_sched_clock, 32, clksrc.rate);
 
 	if (clocksource_register_hz(&clocksource_gpt, clksrc.rate))
@@ -696,6 +728,7 @@ static int __init omap_timer_init(struct omap_hwmod *oh, void *unused)
 	if (timer_dev_attr)
 		pdata->timer_capability = timer_dev_attr->timer_capability;
 
+	pdata->timer_errata = omap_dm_timer_get_errata();
 	pdata->get_context_loss_count = omap_pm_get_dev_context_loss_count;
 
 	pdev = omap_device_build(name, id, oh, pdata, sizeof(*pdata),