Re: [PATCH] m88ts2022: fix 32bit overflow on filter calc

Re: [PATCH] m88ts2022: fix 32bit overflow on filter calc

[Nibble Max]

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It works with the high symbol rate transponders.

Tested-by: Nibble Max <nibble.max@gmail.com>

>Maximum satellite symbol rate used is 45000000Sps which overflows
>when multiplied by 135. As final calculation result is fraction,
>we could use mult_frac macro in order to keep calculation inside
>32 bit number limits and prevent overflow.
>
>Original bug and fix was provided by Nibble Max. I decided to
>implement it differently as it is now.
>
>Reported-by: Nibble Max <nibble.max@gmail.com>
>Cc: <stable@kernel.org>
>Signed-off-by: Antti Palosaari <crope@iki.fi>
>---
> drivers/media/tuners/m88ts2022.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/drivers/media/tuners/m88ts2022.c b/drivers/media/tuners/m88ts2022.c
>index 40c42de..7a62097 100644
>--- a/drivers/media/tuners/m88ts2022.c
>+++ b/drivers/media/tuners/m88ts2022.c
>@@ -314,7 +314,7 @@ static int m88ts2022_set_params(struct dvb_frontend *fe)
> 	div_min = gdiv28 * 78 / 100;
> 	div_max = clamp_val(div_max, 0U, 63U);
> 
>-	f_3db_hz = c->symbol_rate * 135UL / 200UL;
>+	f_3db_hz = mult_frac(c->symbol_rate, 135, 200);
> 	f_3db_hz +=  2000000U + (frequency_offset_khz * 1000U);
> 	f_3db_hz = clamp(f_3db_hz, 7000000U, 40000000U);
> 
>-- 
>http://palosaari.fi/
>

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[PATCH] m88ts2022: fix 32bit overflow on filter calc

[Antti Palosaari]

Maximum satellite symbol rate used is 45000000Sps which overflows
when multiplied by 135. As final calculation result is fraction,
we could use mult_frac macro in order to keep calculation inside
32 bit number limits and prevent overflow.

Original bug and fix was provided by Nibble Max. I decided to
implement it differently as it is now.

Reported-by: Nibble Max <nibble.max@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Antti Palosaari <crope@iki.fi>
---
 drivers/media/tuners/m88ts2022.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/tuners/m88ts2022.c b/drivers/media/tuners/m88ts2022.c
index 40c42de..7a62097 100644
--- a/drivers/media/tuners/m88ts2022.c
+++ b/drivers/media/tuners/m88ts2022.c
@@ -314,7 +314,7 @@ static int m88ts2022_set_params(struct dvb_frontend *fe)
 	div_min = gdiv28 * 78 / 100;
 	div_max = clamp_val(div_max, 0U, 63U);
 
-	f_3db_hz = c->symbol_rate * 135UL / 200UL;
+	f_3db_hz = mult_frac(c->symbol_rate, 135, 200);
 	f_3db_hz +=  2000000U + (frequency_offset_khz * 1000U);
 	f_3db_hz = clamp(f_3db_hz, 7000000U, 40000000U);
 
-- 
http://palosaari.fi/