linux-kernel - RE: [PATCH] ASoC:pcm512x: Fix divide by zero issue.

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Message-ID: <d68a8abc921f45619e077d52d444a7f7@EMAIL.axentia.se>
Date:	Sun, 22 Mar 2015 21:16:10 +0000
From:	Peter Rosin <peda@...ntia.se>
To:	Howard Mitchell <hm@...edded.co.uk>,
	"broonie@...nel.org" <broonie@...nel.org>
CC:	"tiwai@...e.de" <tiwai@...e.de>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"perex@...ex.cz" <perex@...ex.cz>,
	"corbet@....net" <corbet@....net>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ASoC:pcm512x: Fix divide by zero issue.

Howard Mitchell wrote;
> If den=1 and pllin_rate>20MHz then den and num are adjusted to 0
> causing a divide by zero error a few lines further on. Therefore
> this patch correctly scales num and den such that
> pllin_rate/den < 20MHz as required in the device data sheet.

Yep, the old code is plain broken and never actually ran, we have been
using 16MHz pllin_rate, and I apparently never hit this code path.

> Signed-off-by: Howard Mitchell <hm@...edded.co.uk>

Acked-by: Peter Rosin <peda@...ntia.se>

Cheers,
Peter

> ---
>  sound/soc/codecs/pcm512x.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/codecs/pcm512x.c b/sound/soc/codecs/pcm512x.c
> index 5301c4a..8472099 100644
> --- a/sound/soc/codecs/pcm512x.c
> +++ b/sound/soc/codecs/pcm512x.c
> @@ -713,8 +713,8 @@ static int pcm512x_find_pll_coeff(struct snd_soc_dai
> *dai,
> 
>  	/* pllin_rate / P (or here, den) cannot be greater than 20 MHz */
>  	if (pllin_rate / den > 20000000 && num < 8) {
> -		num *= 20000000 / (pllin_rate / den);
> -		den *= 20000000 / (pllin_rate / den);
> +		num *= DIV_ROUND_UP(pllin_rate / den, 20000000);
> +		den *= DIV_ROUND_UP(pllin_rate / den, 20000000);
>  	}
>  	dev_dbg(dev, "num / den = %lu / %lu\n", num, den);
> 
> --
> 1.7.9.5

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