[PATCH v2] rtc: spacemit: handle regmap_test_bits() error return

[kr494167@gmail.com]

From: Surendra Singh Chouhan <kr494167@gmail.com>

p1_rtc_read_time() called if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
to check if the RTC was enabled.

regmap_test_bits() returns 1 if the bit is set, 0 if not set, and a
negative error code (e.g. -EIO) if reading the control register fails.
Using !regmap_test_bits(...) evaluates a negative error code as boolean
false, causing I2C/regmap read failures to be ignored and incorrectly
proceeding to read time registers from a failing device.

Fix this by capturing the return value of regmap_test_bits() and returning
the error code if negative, or -EINVAL if the RTC is disabled.

Fixes: a6de182daa2b ("rtc: spacemit: support the SpacemiT P1 RTC")
Reviewed-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Surendra Singh Chouhan <kr494167@gmail.com>
---
v2:
 - Use ternary shorthand (ret ?: -EINVAL) as suggested by Alex Elder.
 - Collect Reviewed-by tag from Alex Elder.

 drivers/rtc/rtc-spacemit-p1.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-spacemit-p1.c b/drivers/rtc/rtc-spacemit-p1.c
index 43ab62494bb4..1de7bd995d29 100644
--- a/drivers/rtc/rtc-spacemit-p1.c
+++ b/drivers/rtc/rtc-spacemit-p1.c
@@ -57,8 +57,9 @@ static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
 	u8 time[6];
 	int ret;
 
-	if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
-		return -EINVAL;		/* RTC is disabled */
+	ret = regmap_test_bits(regmap, RTC_CTRL, RTC_EN);
+	if (ret <= 0)
+		return ret ?: -EINVAL;	/* RTC is disabled or error */
 
 	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
 	if (ret)
-- 
2.55.0