linux-kernel - Re: [PATCH 3/3] hwmon: (dell-smm) Warn if SMM call took a very long time to execute

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Date:   Tue, 26 Apr 2022 13:17:55 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Armin Wolf <W_Armin@....de>
Cc:     pali@...nel.org, jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] hwmon: (dell-smm) Warn if SMM call took a very long
 time to execute

On Tue, Apr 26, 2022 at 10:03:20PM +0200, Armin Wolf wrote:
> If a particular SMM call takes a very long time to execute,
> the user might experience audio problems. Print a warning
> if a particular SMM call took over 0.250 seconds to execute,
> so the user can check whether or not possible audio problems
> are caused by this driver.
> 
> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>  drivers/hwmon/dell-smm-hwmon.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index f13902414615..b960330eaded 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -49,6 +49,9 @@
>  #define I8K_SMM_GET_DELL_SIG1	0xfea3
>  #define I8K_SMM_GET_DELL_SIG2	0xffa3
> 
> +/* in usecs */
> +#define DELL_SMM_MAX_DURATION  250000
> +
>  #define I8K_FAN_MULT		30
>  #define I8K_FAN_RPM_THRESHOLD	1000
>  #define I8K_MAX_TEMP		127
> @@ -239,6 +242,9 @@ static int i8k_smm_func(void *par)
>  	pr_debug("smm(0x%.4x 0x%.4x) = 0x%.4x  (took %7lld usecs)\n", eax, ebx,
>  		 (rc ? 0xffff : regs->eax & 0xffff), duration);
> 
> +	if (duration > DELL_SMM_MAX_DURATION)
> +		pr_warn("SMM call took %lld usecs!\n", duration);

pr_warn_once, maybe ? If this happens, it will happen a lot, and it doesn't
add much if any value to keep reporting the problem.

Guenter