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authorRonald Wahl <ronald.wahl@raritan.com>2023-10-07 18:17:13 +0200
committerDaniel Lezcano <daniel.lezcano@linaro.org>2023-10-13 12:56:50 +0200
commit6d3bc4c02d59996d1d3180d8ed409a9d7d5900e0 (patch)
treeffcd0e92cfdd26fe3a8db7a8200663130ce84d30 /drivers/clocksource
parentclocksource/timer-riscv: ACPI: Add timer_cannot_wakeup_cpu (diff)
downloadlinux-6d3bc4c02d59996d1d3180d8ed409a9d7d5900e0.tar.xz
linux-6d3bc4c02d59996d1d3180d8ed409a9d7d5900e0.zip
clocksource/drivers/timer-atmel-tcb: Fix initialization on SAM9 hardware
On SAM9 hardware two cascaded 16 bit timers are used to form a 32 bit high resolution timer that is used as scheduler clock when the kernel has been configured that way (CONFIG_ATMEL_CLOCKSOURCE_TCB). The driver initially triggers a reset-to-zero of the two timers but this reset is only performed on the next rising clock. For the first timer this is ok - it will be in the next 60ns (16MHz clock). For the chained second timer this will only happen after the first timer overflows, i.e. after 2^16 clocks (~4ms with a 16MHz clock). So with other words the scheduler clock resets to 0 after the first 2^16 clock cycles. It looks like that the scheduler does not like this and behaves wrongly over its lifetime, e.g. some tasks are scheduled with a long delay. Why that is and if there are additional requirements for this behaviour has not been further analysed. There is a simple fix for resetting the second timer as well when the first timer is reset and this is to set the ATMEL_TC_ASWTRG_SET bit in the Channel Mode register (CMR) of the first timer. This will also rise the TIOA line (clock input of the second timer) when a software trigger respective SYNC is issued. Signed-off-by: Ronald Wahl <ronald.wahl@raritan.com> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Link: https://lore.kernel.org/r/20231007161803.31342-1-rwahl@gmx.de
Diffstat (limited to 'drivers/clocksource')
-rw-r--r--drivers/clocksource/timer-atmel-tcb.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/clocksource/timer-atmel-tcb.c b/drivers/clocksource/timer-atmel-tcb.c
index 27af17c99590..2a90c92a9182 100644
--- a/drivers/clocksource/timer-atmel-tcb.c
+++ b/drivers/clocksource/timer-atmel-tcb.c
@@ -315,6 +315,7 @@ static void __init tcb_setup_dual_chan(struct atmel_tc *tc, int mck_divisor_idx)
writel(mck_divisor_idx /* likely divide-by-8 */
| ATMEL_TC_WAVE
| ATMEL_TC_WAVESEL_UP /* free-run */
+ | ATMEL_TC_ASWTRG_SET /* TIOA0 rises at software trigger */
| ATMEL_TC_ACPA_SET /* TIOA0 rises at 0 */
| ATMEL_TC_ACPC_CLEAR, /* (duty cycle 50%) */
tcaddr + ATMEL_TC_REG(0, CMR));