[PATCH v2] clocksource: timer-riscv: Clear timer interrupt on timer initialization

[PATCH v2] clocksource: timer-riscv: Clear timer interrupt on timer initialization

[Ley Foon Tan]

In the RISC-V specification, the stimecmp register doesn't have a default
value. To prevent the timer interrupt from being triggered during timer
initialization, clear the timer interrupt by writing stimecmp with a
maximum value.

Fixes: 9f7a8ff6391f ("RISC-V: Prefer sstc extension if available")
Cc:  <stable@vger.kernel.org>
Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>

---
v2:
Resolved comments from Anup.
- Moved riscv_clock_event_stop() to riscv_timer_starting_cpu().
- Added Fixes tag
---
 drivers/clocksource/timer-riscv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index e66dcbd66566..672669eb7281 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -116,6 +116,9 @@ static int riscv_timer_starting_cpu(unsigned int cpu)
 		ce->rating = 450;
 	clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
 
+	/* Clear timer interrupt */
+	riscv_clock_event_stop();
+
 	enable_percpu_irq(riscv_clock_event_irq,
 			  irq_get_trigger_type(riscv_clock_event_irq));
 	return 0;
-- 
2.43.0

Re: [PATCH v2] clocksource: timer-riscv: Clear timer interrupt on timer initialization

[Anup Patel]

On Mon, Jan 29, 2024 at 1:12 PM Ley Foon Tan
<leyfoon.tan@starfivetech.com> wrote:
>
> In the RISC-V specification, the stimecmp register doesn't have a default
> value. To prevent the timer interrupt from being triggered during timer
> initialization, clear the timer interrupt by writing stimecmp with a
> maximum value.
>
> Fixes: 9f7a8ff6391f ("RISC-V: Prefer sstc extension if available")
> Cc:  <stable@vger.kernel.org>
> Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>

LGTM.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

>
> ---
> v2:
> Resolved comments from Anup.
> - Moved riscv_clock_event_stop() to riscv_timer_starting_cpu().
> - Added Fixes tag
> ---
>  drivers/clocksource/timer-riscv.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> index e66dcbd66566..672669eb7281 100644
> --- a/drivers/clocksource/timer-riscv.c
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -116,6 +116,9 @@ static int riscv_timer_starting_cpu(unsigned int cpu)
>                 ce->rating = 450;
>         clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
>
> +       /* Clear timer interrupt */
> +       riscv_clock_event_stop();
> +
>         enable_percpu_irq(riscv_clock_event_irq,
>                           irq_get_trigger_type(riscv_clock_event_irq));
>         return 0;
> --
> 2.43.0
>
>

Re: [PATCH v2] clocksource: timer-riscv: Clear timer interrupt on timer initialization

[Samuel Holland]

On 2024-01-29 1:26 AM, Ley Foon Tan wrote:
> In the RISC-V specification, the stimecmp register doesn't have a default
> value. To prevent the timer interrupt from being triggered during timer
> initialization, clear the timer interrupt by writing stimecmp with a
> maximum value.
> 
> Fixes: 9f7a8ff6391f ("RISC-V: Prefer sstc extension if available")
> Cc:  <stable@vger.kernel.org>
> Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
> 
> ---
> v2:
> Resolved comments from Anup.
> - Moved riscv_clock_event_stop() to riscv_timer_starting_cpu().
> - Added Fixes tag
> ---
>  drivers/clocksource/timer-riscv.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> index e66dcbd66566..672669eb7281 100644
> --- a/drivers/clocksource/timer-riscv.c
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -116,6 +116,9 @@ static int riscv_timer_starting_cpu(unsigned int cpu)
>  		ce->rating = 450;
>  	clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
>  
> +	/* Clear timer interrupt */
> +	riscv_clock_event_stop();

This change breaks boot on Unmatched. The bug is that the above call to
clockevents_config_and_register() sets the timer (see below), but the timer
interrupt never fires due to the added call to riscv_clock_event_stop(). You
need to move this line earlier in the function.

Here's the stack trace from the initial call to riscv_clock_next_event():
riscv_clock_next_event+0x12/0x3c
clockevents_program_event+0x9c/0x1c6
tick_setup_periodic+0x82/0x9e
tick_setup_device+0xa0/0xbe
tick_check_new_device+0x96/0xc6
clockevents_register_device+0xbe/0x128
clockevents_config_and_register+0x20/0x30
riscv_timer_starting_cpu+0xa2/0xec
cpuhp_invoke_callback+0x160/0x61e
cpuhp_issue_call+0x140/0x16e
__cpuhp_setup_state_cpuslocked+0x186/0x2b0
__cpuhp_setup_state+0x3a/0x60
riscv_timer_init_common+0xea/0x184
riscv_timer_init_dt+0xbe/0xc2
timer_probe+0x70/0xdc
time_init+0x74/0xa0
start_kernel+0x194/0x35e

Regards,
Samuel

> +
>  	enable_percpu_irq(riscv_clock_event_irq,
>  			  irq_get_trigger_type(riscv_clock_event_irq));
>  	return 0;