[PATCH] ARM: 2701/1: free up ixp2000 timer 4 for the watchdog

Patch from Lennert Buytenhek

The IXP2000 has four timers, but if we're on an A-step IXP2800, timer
2 and 3 don't work.  We need two timers for timekeeping (one for the
timer interrupt and one for tracking missed jiffies), so on early
IXP2800s we have no other choice but to use timer 1 and 4 for that,
but on all other IXP2000s we'd rather leave timer 4 free since that's
the only timer we can use for the watchdog.
So, on buggy IXP2000s (i.e. the A-step IXP2800) we use timer 4 for
tracking missed jiffies, and on all all non-buggy IXP2000s (i.e.
everything but the A-step IXP2800) we use timer 2.
On a pre-production IXP2800, this patch should print these messages
on boot:
	Enabling IXP2800 erratum #25 workaround
	Unable to use IXP2000 watchdog due to IXP2800 erratum #25
On any non-buggy IXP2800 (as well as on IXP2400s) you shouldn't see
anything at all, and the watchdog should be usable again.

Signed-off-by: Lennert Buytenhek
Signed-off-by: Deepak Saxena
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 26 insertions, 8 deletions

diff --git a/arch/arm/mach-ixp2000/core.c b/arch/arm/mach-ixp2000/core.c
index 4f3c3d5c781c..fc0555596d6d 100644
--- a/arch/arm/mach-ixp2000/core.c
+++ b/arch/arm/mach-ixp2000/core.c
@@ -162,12 +162,13 @@ void __init ixp2000_map_io(void)
 static unsigned ticks_per_jiffy;
 static unsigned ticks_per_usec;
 static unsigned next_jiffy_time;
+static volatile unsigned long *missing_jiffy_timer_csr;
 
 unsigned long ixp2000_gettimeoffset (void)
 {
         unsigned long offset;
 
-        offset = next_jiffy_time - *IXP2000_T4_CSR;
+        offset = next_jiffy_time - *missing_jiffy_timer_csr;
 
         return offset / ticks_per_usec;
 }
@@ -179,7 +180,7 @@ static int ixp2000_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
         /* clear timer 1 */
         ixp2000_reg_write(IXP2000_T1_CLR, 1);
         
-        while ((next_jiffy_time - *IXP2000_T4_CSR) > ticks_per_jiffy) {
+        while ((next_jiffy_time - *missing_jiffy_timer_csr) > ticks_per_jiffy) {
                 timer_tick(regs);
                 next_jiffy_time -= ticks_per_jiffy;
         }
@@ -197,20 +198,37 @@ static struct irqaction ixp2000_timer_irq = {
 
 void __init ixp2000_init_time(unsigned long tick_rate)
 {
-        ixp2000_reg_write(IXP2000_T1_CLR, 0);
-        ixp2000_reg_write(IXP2000_T4_CLR, 0);
-
         ticks_per_jiffy = (tick_rate + HZ/2) / HZ;
         ticks_per_usec = tick_rate / 1000000;
 
+        /*
+         * We use timer 1 as our timer interrupt.
+         */
+        ixp2000_reg_write(IXP2000_T1_CLR, 0);
         ixp2000_reg_write(IXP2000_T1_CLD, ticks_per_jiffy - 1);
         ixp2000_reg_write(IXP2000_T1_CTL, (1 << 7));
 
         /*
-         * We use T4 as a monotonic counter to track missed jiffies
+         * We use a second timer as a monotonic counter for tracking
+         * missed jiffies.  The IXP2000 has four timers, but if we're
+         * on an A-step IXP2800, timer 2 and 3 don't work, so on those
+         * chips we use timer 4.  Timer 4 is the only timer that can
+         * be used for the watchdog, so we use timer 2 if we're on a
+         * non-buggy chip.
          */
-        ixp2000_reg_write(IXP2000_T4_CLD, -1);
-        ixp2000_reg_write(IXP2000_T4_CTL, (1 << 7));
+        if ((*IXP2000_PRODUCT_ID & 0x001ffef0) == 0x00000000) {
+                printk(KERN_INFO "Enabling IXP2800 erratum #25 workaround\n");
+
+                ixp2000_reg_write(IXP2000_T4_CLR, 0);
+                ixp2000_reg_write(IXP2000_T4_CLD, -1);
+                ixp2000_reg_write(IXP2000_T4_CTL, (1 << 7));
+                missing_jiffy_timer_csr = IXP2000_T4_CSR;
+        } else {
+                ixp2000_reg_write(IXP2000_T2_CLR, 0);
+                ixp2000_reg_write(IXP2000_T2_CLD, -1);
+                ixp2000_reg_write(IXP2000_T2_CTL, (1 << 7));
+                missing_jiffy_timer_csr = IXP2000_T2_CSR;
+        }
         next_jiffy_time = 0xffffffff;
 
         /* register for interrupt */