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Message-ID: <b56e07aa-526c-4cf1-9e39-474aac78a844@roeck-us.net>
Date: Thu, 30 Nov 2023 20:12:56 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Armin Wolf <W_Armin@....de>
Cc: jdelvare@...e.com, linux-hwmon@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (acpi_power_meter) Fix 4.29 MW bug
On Fri, Nov 24, 2023 at 07:27:47PM +0100, Armin Wolf wrote:
> The ACPI specification says:
>
> "If an error occurs while obtaining the meter reading or if the value
> is not available then an Integer with all bits set is returned"
>
> Since the "integer" is 32 bits in case of the ACPI power meter,
> userspace will get a power reading of 2^32 * 1000 miliwatts (~4.29 MW)
> in case of such an error. This was discovered due to a lm_sensors
> bugreport (https://github.com/lm-sensors/lm-sensors/issues/460).
> Fix this by returning -ENODATA instead.
>
> Tested-by: <urbinek@...il.com>
> Fixes: de584afa5e18 ("hwmon driver for ACPI 4.0 power meters")
> Signed-off-by: Armin Wolf <W_Armin@....de>
Applied.
Thanks,
Guenter
> ---
> drivers/hwmon/acpi_power_meter.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> --
> 2.39.2
>
> diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
> index 8db740214ffd..703666b95bf4 100644
> --- a/drivers/hwmon/acpi_power_meter.c
> +++ b/drivers/hwmon/acpi_power_meter.c
> @@ -31,6 +31,7 @@
> #define POWER_METER_CAN_NOTIFY (1 << 3)
> #define POWER_METER_IS_BATTERY (1 << 8)
> #define UNKNOWN_HYSTERESIS 0xFFFFFFFF
> +#define UNKNOWN_POWER 0xFFFFFFFF
>
> #define METER_NOTIFY_CONFIG 0x80
> #define METER_NOTIFY_TRIP 0x81
> @@ -348,6 +349,9 @@ static ssize_t show_power(struct device *dev,
> update_meter(resource);
> mutex_unlock(&resource->lock);
>
> + if (resource->power == UNKNOWN_POWER)
> + return -ENODATA;
> +
> return sprintf(buf, "%llu\n", resource->power * 1000);
> }
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