linux-kernel - Re: [PATCH v3 26/26] media: dvb-frontends: tda10048: Make the range of z explicit.

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Date: Fri, 3 May 2024 11:27:58 +0100
From: Mauro Carvalho Chehab <mchehab@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Martin Tuma <martin.tuma@...iteqautomotive.com>, Laurent Pinchart
 <laurent.pinchart@...asonboard.com>, Hugues Fruchet
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Subject: Re: [PATCH v3 26/26] media: dvb-frontends: tda10048: Make the range
 of z explicit.

Em Mon, 29 Apr 2024 15:05:05 +0000
Ricardo Ribalda <ribalda@...omium.org> escreveu:

> We do not expect the sample_freq to be over 613MHz.
> 
> Found by cocci:
> drivers/media/dvb-frontends/tda10048.c:345:1-7: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/dvb-frontends/tda10048.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/dvb-frontends/tda10048.c b/drivers/media/dvb-frontends/tda10048.c
> index 3e725cdcc66b..1886f733dbbf 100644
> --- a/drivers/media/dvb-frontends/tda10048.c
> +++ b/drivers/media/dvb-frontends/tda10048.c
> @@ -328,7 +328,8 @@ static int tda10048_set_wref(struct dvb_frontend *fe, u32 sample_freq_hz,
>  			     u32 bw)
>  {
>  	struct tda10048_state *state = fe->demodulator_priv;
> -	u64 t, z;
> +	u32 z;
> +	u64 t;
>  
>  	dprintk(1, "%s()\n", __func__);
>  
> @@ -341,6 +342,7 @@ static int tda10048_set_wref(struct dvb_frontend *fe, u32 sample_freq_hz,
>  	/* t *= 2147483648 on 32bit platforms */
>  	t *= (2048 * 1024);
>  	t *= 1024;
> +	/* Sample frequency is under 613MHz */

Are you sure about that? Some DVB devices have very high frequency 
clocks, specially if they're also used for satellite, so I can't
be sure by just looking at the driver's code.

Also, we had already a bunch of regressions with "fixes" like this
that actually broke frontend drivers.

If you're sure, please add a note at the description mentioning 
on what part of the datasheet you got it.

Otherwise, let's stick with the current code and address cocci
warning on a different way.

Regards,
Mauro

PS.: I partially applied this patch series. I left a few
patches out of the merge to let other people review/comment
(and/or for me to take a deeper look later on).

Regards,
Mauro