Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection

[Guenter Roeck <linux@roeck-us.net>]

On 05/21/2016 07:46 AM, Pali Rohár wrote:
> On more Dell machines (e.g. Dell Precision M3800) I8K_SMM_GET_FAN_TYPE call
> is too expensive (CPU is too long in SMM mode) and cause kernel to hang.
> This patch cache type for each fan (as it should not change) and change the
> way how fan presense is detected. It revert and use function fan_status()
> as was before commit f989e55452c7 ("i8k: Add support for fan labels").
>
> Moreover, kernel hangs for 2 - 3 seconds only sometimes and only on some
> Dell machines. When kernel hangs fan speed is at max. So it was hard to
> debug and bisect where is root of this problem. It looks like this is bug
> in Dell BIOS which implement fan type SMM code... and there is no way how
> to fix it in kernel.
>
> Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
> Reviewed-by: Jean Delvare <jdelvare@suse.de>
> Reported-and-tested-by: Tolga Cakir <cevelnet@gmail.com>
> Fixes: f989e55452c7 ("i8k: Add support for fan labels")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=112021
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=100121
> Cc: stable@vger.kernel.org # v4.0+, will need backport

Should this patch be applied, or do you wait for more testing ?

Guenter

> ---
>   drivers/hwmon/dell-smm-hwmon.c |   21 ++++++++++++++++-----
>   1 file changed, 16 insertions(+), 5 deletions(-)
> ---
>
> Hi!
>
> Jan C Peters, Thorsten Leemhuis, David Santamaría Rogado, Peter Saunderson
> and others, can you test this patch if it fixes your freeze problem at
> boottime and when using "sensors" program?
>
> I need to know if this patch fixes problem on Dell Studio XPS 8000 and
> Dell Studio XPS 8100 machines, so we can revert git commits:
>
> 6220f4ebd7b4 ("hwmon: (dell-smm) Blacklist Dell Studio XPS 8000")
> a4b45b25f18d ("hwmon: (dell-smm) Blacklist Dell Studio XPS 8100")
>
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index c43318d..577445f 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -235,7 +235,7 @@ static int i8k_get_fan_speed(int fan)
>   /*
>    * Read the fan type.
>    */
> -static int i8k_get_fan_type(int fan)
> +static int _i8k_get_fan_type(int fan)
>   {
>   	struct smm_regs regs = { .eax = I8K_SMM_GET_FAN_TYPE, };
>
> @@ -243,6 +243,17 @@ static int i8k_get_fan_type(int fan)
>   	return i8k_smm(&regs) ? : regs.eax & 0xff;
>   }
>
> +static int i8k_get_fan_type(int fan)
> +{
> +	/* I8K_SMM_GET_FAN_TYPE SMM call is expensive, so cache values */
> +	static int types[2] = { INT_MIN, INT_MIN };
> +
> +	if (types[fan] == INT_MIN)
> +		types[fan] = _i8k_get_fan_type(fan);
> +
> +	return types[fan];
> +}
> +
>   /*
>    * Read the fan nominal rpm for specific fan speed.
>    */
> @@ -767,13 +778,13 @@ static int __init i8k_init_hwmon(void)
>   	if (err >= 0)
>   		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP4;
>
> -	/* First fan attributes, if fan type is OK */
> -	err = i8k_get_fan_type(0);
> +	/* First fan attributes, if fan status is OK */
> +	err = i8k_get_fan_status(0);
>   	if (err >= 0)
>   		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN1;
>
> -	/* Second fan attributes, if fan type is OK */
> -	err = i8k_get_fan_type(1);
> +	/* Second fan attributes, if fan status is OK */
> +	err = i8k_get_fan_status(1);
>   	if (err >= 0)
>   		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN2;
>
>