[PATCH] ASoC: nau8824: use 64-bit arithmetic instead of 32-bit

[PATCH] ASoC: nau8824: use 64-bit arithmetic instead of 32-bit

[Gustavo A. R. Silva]

Add suffix ULL to constant 256 in order to give the compiler complete
information about the proper arithmetic to use.

Notice that such constant is used in a context that expects an
expression of type u64 (64 bits, unsigned) and the following
expression is currently being evaluated using 32-bit arithmetic:

256 * fs * 2 * mclk_src_scaling[i].param

Addresses-Coverity-ID: 1432039 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 sound/soc/codecs/nau8824.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/codecs/nau8824.c b/sound/soc/codecs/nau8824.c
index 6bd1445..468d514 100644
--- a/sound/soc/codecs/nau8824.c
+++ b/sound/soc/codecs/nau8824.c
@@ -1274,7 +1274,7 @@ static int nau8824_calc_fll_param(unsigned int fll_in,
 	fvco_max = 0;
 	fvco_sel = ARRAY_SIZE(mclk_src_scaling);
 	for (i = 0; i < ARRAY_SIZE(mclk_src_scaling); i++) {
-		fvco = 256 * fs * 2 * mclk_src_scaling[i].param;
+		fvco = 256ULL * fs * 2 * mclk_src_scaling[i].param;
 		if (fvco > NAU_FVCO_MIN && fvco < NAU_FVCO_MAX &&
 			fvco_max < fvco) {
 			fvco_max = fvco;
-- 
2.7.4

Applied "ASoC: nau8824: use 64-bit arithmetic instead of 32-bit" to the asoc tree

[Mark Brown]

The patch

   ASoC: nau8824: use 64-bit arithmetic instead of 32-bit

has been applied to the asoc tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From f7ddff54d0a0f068442414b48bec7f22aa777de7 Mon Sep 17 00:00:00 2001
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Thu, 5 Jul 2018 08:06:17 -0500
Subject: [PATCH] ASoC: nau8824: use 64-bit arithmetic instead of 32-bit

Add suffix ULL to constant 256 in order to give the compiler complete
information about the proper arithmetic to use.

Notice that such constant is used in a context that expects an
expression of type u64 (64 bits, unsigned) and the following
expression is currently being evaluated using 32-bit arithmetic:

256 * fs * 2 * mclk_src_scaling[i].param

Addresses-Coverity-ID: 1432039 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 sound/soc/codecs/nau8824.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/codecs/nau8824.c b/sound/soc/codecs/nau8824.c
index 6bd14453f06e..468d5143e2c4 100644
--- a/sound/soc/codecs/nau8824.c
+++ b/sound/soc/codecs/nau8824.c
@@ -1274,7 +1274,7 @@ static int nau8824_calc_fll_param(unsigned int fll_in,
 	fvco_max = 0;
 	fvco_sel = ARRAY_SIZE(mclk_src_scaling);
 	for (i = 0; i < ARRAY_SIZE(mclk_src_scaling); i++) {
-		fvco = 256 * fs * 2 * mclk_src_scaling[i].param;
+		fvco = 256ULL * fs * 2 * mclk_src_scaling[i].param;
 		if (fvco > NAU_FVCO_MIN && fvco < NAU_FVCO_MAX &&
 			fvco_max < fvco) {
 			fvco_max = fvco;
-- 
2.18.0.rc2

Re: [alsa-devel] [PATCH] ASoC: nau8824: use 64-bit arithmetic instead of 32-bit

[Trent Piepho]

On Thu, Jul 5, 2018 at 6:06 AM, Gustavo A. R. Silva
<gustavo@embeddedor.com> wrote:
> Add suffix ULL to constant 256 in order to give the compiler complete
> information about the proper arithmetic to use.
>
> Notice that such constant is used in a context that expects an
> expression of type u64 (64 bits, unsigned) and the following
> expression is currently being evaluated using 32-bit arithmetic:
>
> 256 * fs * 2 * mclk_src_scaling[i].param
>
> Addresses-Coverity-ID: 1432039 ("Unintentional integer overflow")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  sound/soc/codecs/nau8824.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/soc/codecs/nau8824.c b/sound/soc/codecs/nau8824.c
> index 6bd1445..468d514 100644
> --- a/sound/soc/codecs/nau8824.c
> +++ b/sound/soc/codecs/nau8824.c
> @@ -1274,7 +1274,7 @@ static int nau8824_calc_fll_param(unsigned int fll_in,
>         fvco_max = 0;
>         fvco_sel = ARRAY_SIZE(mclk_src_scaling);
>         for (i = 0; i < ARRAY_SIZE(mclk_src_scaling); i++) {
> -               fvco = 256 * fs * 2 * mclk_src_scaling[i].param;
> +               fvco = 256ULL * fs * 2 * mclk_src_scaling[i].param;

This would be better written as fvco = (256 * 2 *
mclk_src_scaling[i].param) * (u64)fs;

There no reason the entire expression must use 64 bit multiplies,
since the left side
above is know to fit in 32-bits.

The code could be more efficient if mclk_src_scaling had been sorted
by scaling ratio
instead of register value.  In fact, most of the math in this loop
could be precomputed by the
compiler if one instead though of min and max fs range for a given scaler.