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

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

[kr494167]

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")
Signed-off-by: Surendra Singh Chouhan <kr494167@gmail.com>
---
 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..c1820c920ba3 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 ? ret : -EINVAL;	/* RTC is disabled or error */
 
 	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
 	if (ret)
-- 
2.55.0

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

[Alex Elder]

On 7/23/26 9:42 PM, kr494167@gmail.com wrote:
> 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")
> Signed-off-by: Surendra Singh Chouhan <kr494167@gmail.com>

This is an I2C-based regmap, so yes, we do need to test
for errors when reading or writing registers.

I think this is a good fix.  I have a minor suggestion or
two below but either way:

Reviewed-by: Alex Elder <elder@riscstar.com>

> ---
>   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..c1820c920ba3 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 ? ret : -EINVAL;	/* RTC is disabled or error */

Since regmap_test_bits() can return -EINVAL, I wonder if a
different error code would be better to indicate "disabled".
It can return -EBUSY and -EIO too, as well as anything any
regmap->reg_read() can return.  Scanning through the list of
basic error codes I don't have a good suggestion, unfortunately.

Otherwise, perhaps just:

		return ret ? : -EINVAL;  /* comment if you like */

>   
>   	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
>   	if (ret)

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

[Alexandre Belloni]

On 24/07/2026 08:32:13-0500, Alex Elder wrote:
> On 7/23/26 9:42 PM, kr494167@gmail.com wrote:
> > 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")
> > Signed-off-by: Surendra Singh Chouhan <kr494167@gmail.com>
> 
> This is an I2C-based regmap, so yes, we do need to test
> for errors when reading or writing registers.
> 
> I think this is a good fix.  I have a minor suggestion or
> two below but either way:
> 
> Reviewed-by: Alex Elder <elder@riscstar.com>
> 
> > ---
> >   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..c1820c920ba3 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 ? ret : -EINVAL;	/* RTC is disabled or error */
> 
> Since regmap_test_bits() can return -EINVAL, I wonder if a
> different error code would be better to indicate "disabled".
> It can return -EBUSY and -EIO too, as well as anything any
> regmap->reg_read() can return.  Scanning through the list of
> basic error codes I don't have a good suggestion, unfortunately.
> 

No, EINVAL is standard across all the drivers. I considered changing
this to ETIME or ENODATA but that would break userspace too much.

> Otherwise, perhaps just:
> 
> 		return ret ? : -EINVAL;  /* comment if you like */
> 
> >   	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
> >   	if (ret)
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com