[PATCH] hwmon: (mcp9982) Update the interval cache only after successful writes

[PATCH] hwmon: (mcp9982) Update the interval cache only after successful writes

[Baek Kyu, Kim]

mcp9982_write() updates interval_idx before writing the conversion-rate
register. If the write fails without changing the register, subsequent
update_interval reads report the requested interval instead of the
previous setting.

Update interval_idx only after regmap_write() succeeds, leaving the
previous cached interval in place on error.

Fixes: e2fe950f34e5 ("hwmon: add support for MCP998X")
Signed-off-by: Baek Kyu, Kim <pocj8ur4in@gmail.com>
---
Tested under ARM64 QEMU with an emulated SMBus adapter through the hwmon
sysfs interface. Rejected writes reproduce the incorrect interval;
the fix retains the previous value. Successful writes, retries and
MCP9982D's interval limit were also checked. No physical sensor was tested.

 drivers/hwmon/mcp9982.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/mcp9982.c b/drivers/hwmon/mcp9982.c
index 3918dc36c946..2cd41dcbd9af 100644
--- a/drivers/hwmon/mcp9982.c
+++ b/drivers/hwmon/mcp9982.c
@@ -624,6 +624,7 @@ static int mcp9982_write(struct device *dev, enum hwmon_sensor_types type, u32 a
 {
 	struct mcp9982_priv *priv = dev_get_drvdata(dev);
 	unsigned int idx;
+	int ret;
 	u8 addr;
 
 	switch (type) {
@@ -640,9 +641,13 @@ static int mcp9982_write(struct device *dev, enum hwmon_sensor_types type, u32 a
 
 			idx = find_closest_descending(val, mcp9982_update_interval,
 						      ARRAY_SIZE(mcp9982_update_interval));
+			ret = regmap_write(priv->regmap, MCP9982_CONV_ADDR, idx);
+			if (ret)
+				return ret;
+
 			priv->interval_idx = idx;
 
-			return regmap_write(priv->regmap, MCP9982_CONV_ADDR, idx);
+			return 0;
 		default:
 			return -EINVAL;
 		}

base-commit: 58161ead29e50d70a317ea26b472e0c7508e69da
-- 
2.55.0

Re: [PATCH] hwmon: (mcp9982) Update the interval cache only after successful writes

[Victor.Duicu]

On Sun, 2026-10-18 at 14:57 +0900, Baek Kyu, Kim wrote:
> mcp9982_write() updates interval_idx before writing the
> conversion-rate
> register. If the write fails without changing the register,
> subsequent
> update_interval reads report the requested interval instead of the
> previous setting.
> 
> Update interval_idx only after regmap_write() succeeds, leaving the
> previous cached interval in place on error.
> 
> Fixes: e2fe950f34e5 ("hwmon: add support for MCP998X")
> Signed-off-by: Baek Kyu, Kim <pocj8ur4in@gmail.com>
> ---
> Tested under ARM64 QEMU with an emulated SMBus adapter through the
> hwmon
> sysfs interface. Rejected writes reproduce the incorrect interval;
> the fix retains the previous value. Successful writes, retries and
> MCP9982D's interval limit were also checked. No physical sensor was
> tested.
> 
>  drivers/hwmon/mcp9982.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/mcp9982.c b/drivers/hwmon/mcp9982.c
> index 3918dc36c946..2cd41dcbd9af 100644
> --- a/drivers/hwmon/mcp9982.c
> +++ b/drivers/hwmon/mcp9982.c
> @@ -624,6 +624,7 @@ static int mcp9982_write(struct device *dev, enum
> hwmon_sensor_types type, u32 a
>  {
>         struct mcp9982_priv *priv = dev_get_drvdata(dev);
>         unsigned int idx;
> +       int ret;
>         u8 addr;
> 
>         switch (type) {
> @@ -640,9 +641,13 @@ static int mcp9982_write(struct device *dev,
> enum hwmon_sensor_types type, u32 a
> 
>                         idx = find_closest_descending(val,
> mcp9982_update_interval,
>                                                      
> ARRAY_SIZE(mcp9982_update_interval));
> +                       ret = regmap_write(priv->regmap,
> MCP9982_CONV_ADDR, idx);
> +                       if (ret)
> +                               return ret;
> +
>                         priv->interval_idx = idx;
> 
> -                       return regmap_write(priv->regmap,
> MCP9982_CONV_ADDR, idx);
> +                       return 0;
>                 default:
>                         return -EINVAL;
>                 }
> 
> base-commit: 58161ead29e50d70a317ea26b472e0c7508e69da
> --
> 2.55.0

Acked-by: Duicu Victor <victor.duicu@microchip.com>

Best regards,
Victor