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Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Thu, 30 Nov 2023 20:12:56 -0800
From:   Guenter Roeck <linux@roeck-us.net>
To:     Armin Wolf <W_Armin@gmx.de>
Cc:     jdelvare@suse.com, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hwmon: (acpi_power_meter) Fix 4.29 MW bug
Message-ID: <b56e07aa-526c-4cf1-9e39-474aac78a844@roeck-us.net>
References: <20231124182747.13956-1-W_Armin@gmx.de>
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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@gmail.com>
> Fixes: de584afa5e18 ("hwmon driver for ACPI 4.0 power meters")
> Signed-off-by: Armin Wolf <W_Armin@gmx.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);
>  }