linux-kernel - Re: [PATCH] MIPS: cevt-r4k: Don't call get_c0_compare

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Message-ID: <a9ccd0cd-82ee-4e31-9815-f8f3871b30c8@linaro.org>
Date: Fri, 16 Aug 2024 13:40:11 +0200
From: Philippe Mathieu-Daudé <philmd@...aro.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
 Serge Semin <fancer.lancer@...il.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH] MIPS: cevt-r4k: Don't call get_c0_compare_int if timer
 irq is installed

Hi Jiaxun,

+Daniel/Thomas for CLOCKEVENTS

On 13/8/24 11:59, Jiaxun Yang wrote:
> This avoids warning:
> 
> [    0.118053] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:283
> 
> Caused by get_c0_compare_int on secondary CPU.
> 
> We also skipped saving IRQ number to struct clock_event_device *cd as
> it's never used by clockevent core, as per comments it's only meant
> for "non CPU local devices".
> 
> Reported-by: Serge Semin <fancer.lancer@...il.com>
> Closes: https://lore.kernel.org/linux-mips/6szkkqxpsw26zajwysdrwplpjvhl5abpnmxgu2xuj3dkzjnvsf@4daqrz4mf44k/
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
>   arch/mips/kernel/cevt-r4k.c | 15 +++++++--------
>   1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
> index 368e8475870f..5f6e9e2ebbdb 100644
> --- a/arch/mips/kernel/cevt-r4k.c
> +++ b/arch/mips/kernel/cevt-r4k.c
> @@ -303,13 +303,6 @@ int r4k_clockevent_init(void)
>   	if (!c0_compare_int_usable())
>   		return -ENXIO;
>   
> -	/*
> -	 * With vectored interrupts things are getting platform specific.
> -	 * get_c0_compare_int is a hook to allow a platform to return the
> -	 * interrupt number of its liking.
> -	 */
> -	irq = get_c0_compare_int();
> -
>   	cd = &per_cpu(mips_clockevent_device, cpu);
>   
>   	cd->name		= "MIPS";
> @@ -320,7 +313,6 @@ int r4k_clockevent_init(void)
>   	min_delta		= calculate_min_delta();
>   
>   	cd->rating		= 300;
> -	cd->irq			= irq;

What should be the unset value is not clear, clock_event_device::irq
is an int, described in <linux/clockchips.h> as:

   @irq:          IRQ number (only for non CPU local devices)

Most arch clocks set irq > 0 or don't set it.

Core code / drivers check for irq != -1, irq != 0 or irq >= 0:

kernel/time/tick-common.c-295-  if (newdev->irq >= 0 && 
!irq_can_set_affinity(newdev->irq))
kernel/time/tick-common.c-296-          return false;
drivers/clocksource/exynos_mct.c-479-           if (evt->irq == -1)
drivers/clocksource/exynos_mct.c-480-                   return -EIO;
drivers/clocksource/timer-ti-dm-systimer.c-562- if (!dev->irq)
drivers/clocksource/timer-ti-dm-systimer.c-563-         return -ENXIO;

Using -1 for unset value seems reasonable, but since most don't set
this default value, I guess that's OK to do the same.

Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>

>   	cd->cpumask		= cpumask_of(cpu);
>   	cd->set_next_event	= mips_next_event;
>   	cd->event_handler	= mips_event_handler;
> @@ -332,6 +324,13 @@ int r4k_clockevent_init(void)
>   
>   	cp0_timer_irq_installed = 1;
>   
> +	/*
> +	 * With vectored interrupts things are getting platform specific.
> +	 * get_c0_compare_int is a hook to allow a platform to return the
> +	 * interrupt number of its liking.
> +	 */
> +	irq = get_c0_compare_int();
> +
>   	if (request_irq(irq, c0_compare_interrupt, flags, "timer",
>   			c0_compare_interrupt))
>   		pr_err("Failed to request irq %d (timer)\n", irq);
> 
> ---
> base-commit: 9e6869691724b12e1f43655eeedc35fade38120c
> change-id: 20240812-get_c0_compare_int-66935853a308
> 
> Best regards,