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From: Jonathan Cameron <jic23@kernel.org>
To: Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com>
Cc: knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net,
	michal.simek@xilinx.com, git@xilinx.com,
	linux-iio@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, anandash@xilinx.com
Subject: Re: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values
Date: Sat, 29 Aug 2020 16:19:00 +0100	[thread overview]
Message-ID: <20200829161900.713541cd@archlinux> (raw)
In-Reply-To: <1598465676-28912-1-git-send-email-anand.ashok.dumbre@xilinx.com>

On Wed, 26 Aug 2020 11:14:36 -0700
Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com> wrote:

> Fixes IIO_VAL_FRACTIONAL for case when the result is negative and
> exponent is 0.
> 
> example: if the result is -0.75, tmp0 will be 0 and tmp1 = 75
> This causes the output to lose sign because of %d in snprintf
> which works for tmp0 <= -1.
> 
> Signed-off-by: Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com>

Looks good.  Just one last thing.

Is this actually hit in an existing driver?  I'm just wondering
how far back we need to push it in stable etc.

Thanks,

Jonathan

> ---
> changes since v1:
> 	Changed -%d to -0 to make the fix clearer.
> 	Removed the email footer.
> 	Updated the commit description with an example
> --
>  drivers/iio/industrialio-core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index cdcd16f1..a239fa2 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -592,6 +592,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
>  {
>  	unsigned long long tmp;
>  	int tmp0, tmp1;
> +	s64 tmp2;
>  	bool scale_db = false;
>  
>  	switch (type) {
> @@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
>  		else
>  			return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]);
>  	case IIO_VAL_FRACTIONAL:
> -		tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> +		tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
>  		tmp1 = vals[1];
>  		tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
> -		return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> +		if ((tmp2 < 0) && (tmp0 == 0))
> +			return snprintf(buf, len, "-0.%09u", abs(tmp1));
> +		else
> +			return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
>  	case IIO_VAL_FRACTIONAL_LOG2:
>  		tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
>  		tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);


WARNING: multiple messages have this Message-ID (diff)
From: Jonathan Cameron <jic23@kernel.org>
To: Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com>
Cc: lars@metafoo.de, linux-iio@vger.kernel.org,
	michal.simek@xilinx.com, linux-kernel@vger.kernel.org,
	anandash@xilinx.com, git@xilinx.com, pmeerw@pmeerw.net,
	knaack.h@gmx.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values
Date: Sat, 29 Aug 2020 16:19:00 +0100	[thread overview]
Message-ID: <20200829161900.713541cd@archlinux> (raw)
In-Reply-To: <1598465676-28912-1-git-send-email-anand.ashok.dumbre@xilinx.com>

On Wed, 26 Aug 2020 11:14:36 -0700
Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com> wrote:

> Fixes IIO_VAL_FRACTIONAL for case when the result is negative and
> exponent is 0.
> 
> example: if the result is -0.75, tmp0 will be 0 and tmp1 = 75
> This causes the output to lose sign because of %d in snprintf
> which works for tmp0 <= -1.
> 
> Signed-off-by: Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com>

Looks good.  Just one last thing.

Is this actually hit in an existing driver?  I'm just wondering
how far back we need to push it in stable etc.

Thanks,

Jonathan

> ---
> changes since v1:
> 	Changed -%d to -0 to make the fix clearer.
> 	Removed the email footer.
> 	Updated the commit description with an example
> --
>  drivers/iio/industrialio-core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index cdcd16f1..a239fa2 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -592,6 +592,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
>  {
>  	unsigned long long tmp;
>  	int tmp0, tmp1;
> +	s64 tmp2;
>  	bool scale_db = false;
>  
>  	switch (type) {
> @@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
>  		else
>  			return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]);
>  	case IIO_VAL_FRACTIONAL:
> -		tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> +		tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
>  		tmp1 = vals[1];
>  		tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
> -		return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> +		if ((tmp2 < 0) && (tmp0 == 0))
> +			return snprintf(buf, len, "-0.%09u", abs(tmp1));
> +		else
> +			return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
>  	case IIO_VAL_FRACTIONAL_LOG2:
>  		tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
>  		tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);


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  reply	other threads:[~2020-08-29 15:19 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-26 18:14 [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values Anand Ashok Dumbre
2020-08-26 18:14 ` Anand Ashok Dumbre
2020-08-29 15:19 ` Jonathan Cameron [this message]
2020-08-29 15:19   ` Jonathan Cameron
2020-08-31  8:55   ` Anand Ashok Dumbre
2020-08-31  8:55     ` Anand Ashok Dumbre
2020-08-31  9:51 ` Dan Carpenter
2020-08-31  9:51   ` Dan Carpenter
2020-08-31  9:51   ` Dan Carpenter
2020-08-31  9:51   ` Dan Carpenter
2020-08-27  6:41 kernel test robot

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