The time drift problem I have been chasing for a while, see http://linux.davincidsp.com/pipermail/davinci-linux-open-source/2012-December/025821.html , seems to be due to an undocumented silicon bug.
The attached patch to master ( c22cf7755db6500df037cecdd6b290394d82392e Origin: git://gitorious.org/linux-davinci/linux-davinci.git ) exercises the problem. Example console output from my EVM6446 card: ---------------- Before T0:0x5ed55a T1:0x5ed55d Diff:-3 After T0:0x5ed817 T1:0x5ed824 Diff:-13 Before T0:0x62a7e5 T1:0x62a7f3 Diff:-14 After T0:0x62adff T1:0x62ae17 Diff:-24 Before T0:0x66cbfb T1:0x66cc14 Diff:-25 After T0:0x66d1f6 T1:0x66d219 Diff:-35 Before T0:0x6aeab0 T1:0x6aead4 Diff:-36 After T0:0x6af0ec T1:0x6af11a Diff:-46 Before T0:0x6f09ef T1:0x6f0a1e Diff:-47 After T0:0x6f1018 T1:0x6f1051 Diff:-57 Before T0:0x732821 T1:0x73285b Diff:-58 After T0:0x732e1a T1:0x732e5e Diff:-68 --------------- This shows that TIM34_0 misses 11 ticks every time a new event is setup (10 ticks from my test loop + the original code 1). If someone from TI can verify that the problem exists in all Davinci versions, a workaround should be pretty straightforward, assuming this is the only symptom of the bug. Regards, /Thomas
diff --git a/arch/arm/mach-davinci/time.c b/arch/arm/mach-davinci/time.c
index 9847938..95be656 100644
--- a/arch/arm/mach-davinci/time.c
+++ b/arch/arm/mach-davinci/time.c
@@ -117,6 +117,61 @@ static char *id_to_name[] = {
[T1_TOP] = "timer1_1",
};
+/*******************************************************************
+ Test code by tho...@corelatus.se 121212
+ Exercises a timer problem with Davinci, likely a silicon bug.
+ For each write to TIM12, the TIM34 counter misses a tick.
+ With current kernel, this causes time to drift 37 ns every time
+ a new event is set. This can accumulate to 1000 ppms
+ (1 ms per second) if lots of context switches.
+
+ Verified to exist in:
+ DM6443 rev 2.1
+ DM6446 rev 1.3
+*********************************************************************/
+
+static inline void show_timer_diff(const char *str){
+ u32 tim34_0, tim34_1;
+
+ tim34_1 = __raw_readl(IO_ADDRESS(DAVINCI_TIMER1_BASE + TIM34));
+ tim34_0 = __raw_readl(IO_ADDRESS(DAVINCI_TIMER0_BASE + TIM34));
+
+ printk("%s T0:0x%x T1:0x%x Diff:%d\n",
+ str,
+ tim34_0,
+ tim34_1,
+ tim34_0 - tim34_1);
+}
+
+/* When setting up Timer 0-34, setup Timer 1-34 with the same settings.
+ This way, they should always have about the same counter value. */
+static void mirror(struct timer_s *t){
+ /* Timer 1 is +0x400 */
+ volatile void *base = t->base + 0x400;
+ u32 tcr;
+
+ tcr = __raw_readl(base + TCR);
+
+ /* disable timer */
+ tcr &= ~(TCR_ENAMODE_MASK << t->enamode_shift);
+ __raw_writel(tcr, base + TCR);
+
+ /* reset counter to zero, set new period */
+ __raw_writel(0, base + t->tim_off);
+ __raw_writel(t->period, base + t->prd_off);
+
+ /* Set enable mode */
+ if (t->opts & TIMER_OPTS_ONESHOT)
+ tcr |= TCR_ENAMODE_ONESHOT << t->enamode_shift;
+ else if (t->opts & TIMER_OPTS_PERIODIC)
+ tcr |= TCR_ENAMODE_PERIODIC << t->enamode_shift;
+
+ __raw_writel(tcr, base + TCR);
+}
+
+#define CHECK_LAPS 20
+static u32 chk = ~0;
+
static int timer32_config(struct timer_s *t)
{
u32 tcr;
@@ -142,6 +197,19 @@ static int timer32_config(struct timer_s *t)
tcr &= ~(TCR_ENAMODE_MASK << t->enamode_shift);
__raw_writel(tcr, t->base + TCR);
+ if( chk < CHECK_LAPS && t->id == 0 ){
+ int i;
+ show_timer_diff("Before");
+ /* TIM34_0 seems to miss 1 tick every time we write
+ to TIM12_0!
+ So, this loop makes us miss 10 ticks: */
+ for(i=0;i<10;i++){
+ __raw_writel(0, t->base + t->tim_off);
+ }
+ show_timer_diff("After");
+ chk++;
+ }
+
/* reset counter to zero, set new period */
__raw_writel(0, t->base + t->tim_off);
__raw_writel(t->period, t->base + t->prd_off);
@@ -152,6 +220,15 @@ static int timer32_config(struct timer_s *t)
else if (t->opts & TIMER_OPTS_PERIODIC)
tcr |= TCR_ENAMODE_PERIODIC << t->enamode_shift;
+ if(t->id == 1){
+ /* Timer 0-34 setup
+ Setup 1-34 as a mirror to 0-34 */
+ mirror(t);
+
+ /* Start checking TIM counters */
+ chk = 0;
+ }
+
__raw_writel(tcr, t->base + TCR);
}
return 0;
@@ -381,6 +458,10 @@ static void __init davinci_timer_init(void)
BUG_ON(IS_ERR(timer_clk));
clk_prepare_enable(timer_clk);
+ timer_clk = clk_get(NULL, "timer1");
+ BUG_ON(IS_ERR(timer_clk));
+ clk_enable(timer_clk);
+
/* init timer hw */
timer_init();
config.gz
Description: Unix tar archive
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