[PATCH] hwmon: (corsair-cpro) Cache fan target only after a successful command

[PATCH] hwmon: (corsair-cpro) Cache fan target only after a successful command

[Baek Kyu, Kim]

set_target() updates the cached fan target before sending the command.
If the command fails, subsequent fanN_target reads report the failed
request instead of the previous value. For example, after successfully
setting 1200 RPM, a rejected request for 1800 RPM returns an error but
leaves fanN_target reporting 1800. A failed request also replaces
-ENODATA when no target has been successfully set.

Update the target cache under the existing mutex only after
send_usb_cmd() succeeds, as set_pwm() already does when invalidating
the target. Preserve the previous cached value and return the original
error on failure.

Fixes: 40c3a4454225 ("hwmon: add Corsair Commander Pro driver")
Signed-off-by: Baek Kyu, Kim <pocj8ur4in@gmail.com>
---
Tested under ARM64 QEMU with an emulated HID transport through the
actual corsair-cpro driver and hwmon sysfs. Set fan1_target to 1200,
then reject the next 1800 request with -EIO before applying it.
Before the fix, the write fails but readback returns 1800; with the
fix, readback remains 1200. No physical hardware was tested.

 drivers/hwmon/corsair-cpro.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/corsair-cpro.c b/drivers/hwmon/corsair-cpro.c
index c09645152613..f9e8b7a0d70a 100644
--- a/drivers/hwmon/corsair-cpro.c
+++ b/drivers/hwmon/corsair-cpro.c
@@ -214,10 +214,11 @@ static int set_target(struct ccp_device *ccp, int channel, long val)
 	int ret;
 
 	val = clamp_val(val, 0, 0xFFFF);
-	ccp->target[channel] = val;
 
 	mutex_lock(&ccp->mutex);
 	ret = send_usb_cmd(ccp, CTL_SET_FAN_TARGET, channel, val >> 8, val);
+	if (!ret)
+		ccp->target[channel] = val;
 
 	mutex_unlock(&ccp->mutex);
 	return ret;

base-commit: 58161ead29e50d70a317ea26b472e0c7508e69da
-- 
2.55.0