Re: [RESEND PATCH 3/5] platform/x86: bitland-mifs-wmi: read fan tach from EC window on MIFS v2

[Ilpo Järvinen]

On Tue, 28 Jul 2026, 孙 誉铭 wrote:

> The MIFS v2 firmware implements no WMI function for fan speeds (nor
> for the CPU thermometer), so on these machines the hwmon device
> reported zero RPM on every channel.
> 
> The fan tachometers instead live in the EC shared-memory window at
> 0xFE0B0300 (DSDT \_SB.PC00.LPCB.Q_EC region "ERAM") as little-endian
> u16 RPM values at offsets 0x69 and 0x6B (0 = fan stopped). Map the
> window on v2 systems and expose the two fans with proper labels; hide
> the non-existent third fan and temperature channels.
> 
> Offsets verified by diffing the window between idle and sustained load
> (tach values ramp 0 -> ~2700 RPM and back) on a Xiaomi Book Pro 14.
> 
> Signed-off-by: Yuming Sun <wolf109909@xxxxxxxxxxx>
> ---
>  drivers/platform/x86/bitland-mifs-wmi.c | 68 +++++++++++++++++++++++--
>  1 file changed, 65 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/platform/x86/bitland-mifs-wmi.c b/drivers/platform/x86/bitland-mifs-wmi.c
> index 342dd7e1..5f7c85a8 100644
> --- a/drivers/platform/x86/bitland-mifs-wmi.c
> +++ b/drivers/platform/x86/bitland-mifs-wmi.c
> @@ -17,6 +17,7 @@
>  #include <linux/err.h>
>  #include <linux/hwmon.h>
>  #include <linux/init.h>
> +#include <linux/io.h>
>  #include <linux/input-event-codes.h>
>  #include <linux/input.h>
>  #include <linux/input/sparse-keymap.h>
> @@ -151,6 +152,16 @@ struct bitland_mifs_output {
>   */
>  #define MIFS_STATUS_ERROR	0xe000
>  
> +/*
> + * MIFS v2 EC shared-memory window (DSDT \_SB.PC00.LPCB.Q_EC region
> + * "ERAM"). The firmware exposes no WMI fan function, but the fan
> + * tachometers live here as little-endian u16 RPM (0 = fan stopped).
> + */
> +#define MIFS_V2_EC_MEM_BASE	0xFE0B0300
> +#define MIFS_V2_EC_MEM_SIZE	0x100

SZ_xx from sizes.h

> +#define MIFS_V2_EC_REG_FAN1	0x69
> +#define MIFS_V2_EC_REG_FAN2	0x6B
> +
>  static u16 mifs_status(const struct bitland_mifs_output *out)
>  {
>  	return out->reserved1 | (out->operation << 8);
> @@ -188,6 +199,7 @@ struct bitland_mifs_wmi_data {
>  	enum platform_profile_option saved_profile;
>  	bool profile_valid;
>  	bool is_v2;	/* MIFS v2 firmware: QFAN perf-mode codes */
> +	u8 __iomem *ec_mem;	/* v2 EC shared-memory window */
>  };
>  
>  static int bitland_mifs_wmi_call(struct bitland_mifs_wmi_data *data,
> @@ -421,6 +433,27 @@ static const char *const fan_labels[] = {
>  	"SYS", /* 2 */
>  };
>  
> +static const char *const fan_labels_v2[] = {
> +	"Left Fan", /* 0 */
> +	"Right Fan", /* 1 */

Please align comments.

> +};
> +
> +static umode_t laptop_hwmon_visible(const void *drvdata,
> +				    enum hwmon_sensor_types type,
> +				    u32 attr, int channel)
> +{
> +	const struct bitland_mifs_wmi_data *data = drvdata;
> +
> +	/* v2 firmware: two fans, no CPU temperature channel */
> +	if (data->is_v2) {
> +		if (type == hwmon_fan && channel < 2)
> +			return 0444;
> +		return 0;
> +	}
> +
> +	return 0444;
> +}
> +
>  static int laptop_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  			     u32 attr, int channel, long *val)
>  {
> @@ -433,6 +466,22 @@ static int laptop_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  	struct bitland_mifs_output res;
>  	int ret;
>  
> +	/* v2: tachometers are u16 RPM in the EC shared-memory window */
> +	if (data->is_v2) {
> +		if (type != hwmon_fan || !data->ec_mem)
> +			return -EINVAL;

-EINVAL is plain wrong if you failed to initialize ec_mem. There's no 
problem in input parameters whatsoever in that case.

> +		switch (channel) {
> +		case 0:
> +			*val = get_unaligned_le16(data->ec_mem + MIFS_V2_EC_REG_FAN1);
> +			return 0;
> +		case 1:
> +			*val = get_unaligned_le16(data->ec_mem + MIFS_V2_EC_REG_FAN2);
> +			return 0;
> +		default:
> +			return -EINVAL;
> +		}
> +	}
> +
>  	switch (type) {
>  	case hwmon_temp:
>  		input.function = WMI_FN_CPU_THERMOMETER;
> @@ -468,9 +517,13 @@ static int laptop_hwmon_read_string(struct device *dev,
>  				    enum hwmon_sensor_types type, u32 attr,
>  				    int channel, const char **str)
>  {
> +	struct bitland_mifs_wmi_data *data = dev_get_drvdata(dev);
> +	const char *const *labels = data->is_v2 ? fan_labels_v2 : fan_labels;
> +	int nlabels = data->is_v2 ? ARRAY_SIZE(fan_labels_v2) : ARRAY_SIZE(fan_labels);

Looks ugly but I suppose you're going to get rid of is_v2 anyway as per 
somebody else's suggestion so it should try to deal with this I guess.

> +
>  	if (type == hwmon_fan && attr == hwmon_fan_label) {
> -		if (channel >= 0 && channel < ARRAY_SIZE(fan_labels)) {
> -			*str = fan_labels[channel];
> +		if (channel >= 0 && channel < nlabels) {
> +			*str = labels[channel];
>  			return 0;
>  		}
>  	}
> @@ -486,7 +539,7 @@ static const struct hwmon_channel_info *laptop_hwmon_info[] = {
>  };
>  
>  static const struct hwmon_ops laptop_hwmon_ops = {
> -	.visible = 0444,
> +	.is_visible = laptop_hwmon_visible,
>  	.read = laptop_hwmon_read,
>  	.read_string = laptop_hwmon_read_string,
>  };
> @@ -782,6 +835,15 @@ static int bitland_mifs_wmi_probe(struct wmi_device *wdev, const void *context)
>  			dev_info(&wdev->dev,
>  				 "MIFS v2 firmware detected (QFAN mode codes)\n");
>  		}
> +
> +		if (drv_data->is_v2) {
> +			drv_data->ec_mem = devm_ioremap(&wdev->dev,
> +							MIFS_V2_EC_MEM_BASE,
> +							MIFS_V2_EC_MEM_SIZE);
> +			if (!drv_data->ec_mem)
> +				dev_warn(&wdev->dev,
> +					 "cannot map EC window, fan tach unavailable\n");
> +		}
>  	}
>  
>  	if (dev_type == BITLAND_WMI_EVENT) {
> 

-- 
 i.