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authorFinn Thain <fthain@telegraphics.com.au>2018-12-01 11:53:10 +1100
committerGeert Uytterhoeven <geert@linux-m68k.org>2019-03-25 10:22:24 +0100
commit26ccd2d376d9b7de9a27b9a7ed71e16216101921 (patch)
tree514f9e44b8c2ef830c6c0e6a6bfb4d7df2a6b927
parent5afd3d06e5cb30a312aaa34348f9457b9fb38a52 (diff)
m68k: atari: Convert to clocksource API
Add a platform clocksource by adapting the existing arch_gettimeoffset implementation. Normally the MFP timer C interrupt flag would be used to check for timer counter wrap-around. Unfortunately, that flag gets cleared by the MFP itself (due to automatic End-of-Interrupt mode). This means that mfp_timer_c_handler() and atari_read_clk() must race when accounting for counter wrap-around. That problem is avoided by effectively stopping the clock when it might otherwise jump backwards (due to interrupt latency). Note that this may affect clock accuracy. After the timer interrupt is asserted, wait for the counter to be reloaded so that atari_read_clk() will not see the intermediate state as that would cause the clock to jump backwards. Signed-off-by: Finn Thain <fthain@telegraphics.com.au> Acked-by: Linus Walleij <linus.walleij@linaro.org> Tested-by: Michael Schmitz <schmitzmic@gmail.com> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
-rw-r--r--arch/m68k/atari/time.c53
1 files changed, 36 insertions, 17 deletions
diff --git a/arch/m68k/atari/time.c b/arch/m68k/atari/time.c
index fafa20f75ab9..ce923a523695 100644
--- a/arch/m68k/atari/time.c
+++ b/arch/m68k/atari/time.c
@@ -16,6 +16,7 @@
#include <linux/init.h>
#include <linux/rtc.h>
#include <linux/bcd.h>
+#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/export.h>
@@ -24,12 +25,29 @@
DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL_GPL(rtc_lock);
+static u64 atari_read_clk(struct clocksource *cs);
+
+static struct clocksource atari_clk = {
+ .name = "mfp",
+ .rating = 100,
+ .read = atari_read_clk,
+ .mask = CLOCKSOURCE_MASK(32),
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static u32 clk_total;
+static u8 last_timer_count;
+
static irqreturn_t mfp_timer_c_handler(int irq, void *dev_id)
{
irq_handler_t timer_routine = dev_id;
unsigned long flags;
local_irq_save(flags);
+ do {
+ last_timer_count = st_mfp.tim_dt_c;
+ } while (last_timer_count == 1);
+ clk_total += INT_TICKS;
timer_routine(0, NULL);
local_irq_restore(flags);
@@ -44,32 +62,33 @@ atari_sched_init(irq_handler_t timer_routine)
/* start timer C, div = 1:100 */
st_mfp.tim_ct_cd = (st_mfp.tim_ct_cd & 15) | 0x60;
/* install interrupt service routine for MFP Timer C */
- if (request_irq(IRQ_MFP_TIMC, mfp_timer_c_handler, 0, "timer",
+ if (request_irq(IRQ_MFP_TIMC, mfp_timer_c_handler, IRQF_TIMER, "timer",
timer_routine))
pr_err("Couldn't register timer interrupt\n");
+
+ clocksource_register_hz(&atari_clk, INT_CLK);
}
/* ++andreas: gettimeoffset fixed to check for pending interrupt */
-#define TICK_SIZE 10000
-
-/* This is always executed with interrupts disabled. */
-u32 atari_gettimeoffset(void)
+static u64 atari_read_clk(struct clocksource *cs)
{
- u32 ticks, offset = 0;
-
- /* read MFP timer C current value */
- ticks = st_mfp.tim_dt_c;
- /* The probability of underflow is less than 2% */
- if (ticks > INT_TICKS - INT_TICKS / 50)
- /* Check for pending timer interrupt */
- if (st_mfp.int_pn_b & (1 << 5))
- offset = TICK_SIZE;
+ unsigned long flags;
+ u8 count;
+ u32 ticks;
- ticks = INT_TICKS - ticks;
- ticks = ticks * 10000L / INT_TICKS;
+ local_irq_save(flags);
+ /* Ensure that the count is monotonically decreasing, even though
+ * the result may briefly stop changing after counter wrap-around.
+ */
+ count = min(st_mfp.tim_dt_c, last_timer_count);
+ last_timer_count = count;
+
+ ticks = INT_TICKS - count;
+ ticks += clk_total;
+ local_irq_restore(flags);
- return (ticks + offset) * 1000;
+ return ticks;
}