linux-kernel - Re: [PATCH] media: dvb-frontends: use div64_u64() instead of do

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Message-ID: <c78ed114-b838-e030-a235-f4de9c88e71e@xs4all.nl>
Date:   Fri, 18 Feb 2022 11:49:42 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Qing Wang <wangqing@...o.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: dvb-frontends: use div64_u64() instead of do_div()

On 09/02/2022 09:38, Qing Wang wrote:
> From: Wang Qing <wangqing@...o.com>
> 
> do_div() does a 64-by-32 division.
> When the divisor is u64, do_div() truncates it to 32 bits, this means it
> can test non-zero and be truncated to zero for division.
> 
> fix do_div.cocci warning:
> do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> 
> Signed-off-by: Wang Qing <wangqing@...o.com>
> ---
>  drivers/media/dvb-frontends/tda10048.c     | 2 +-
>  drivers/media/dvb-frontends/tda18271c2dd.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/dvb-frontends/tda10048.c b/drivers/media/dvb-frontends/tda10048.c
> index d1d206e..1ce2e67
> --- a/drivers/media/dvb-frontends/tda10048.c
> +++ b/drivers/media/dvb-frontends/tda10048.c
> @@ -344,7 +344,7 @@ static int tda10048_set_wref(struct dvb_frontend *fe, u32 sample_freq_hz,
>  	z = 7 * sample_freq_hz;
>  	do_div(t, z);
>  	t += 5;
> -	do_div(t, 10);
> +	div64_u64(t, 10);

This makes no sense, I think you intended to convert the previous do_div(t, z).

>  
>  	tda10048_writereg(state, TDA10048_TIME_WREF_LSB, (u8)t);
>  	tda10048_writereg(state, TDA10048_TIME_WREF_MID1, (u8)(t >> 8));
> diff --git a/drivers/media/dvb-frontends/tda18271c2dd.c b/drivers/media/dvb-frontends/tda18271c2dd.c
> index a3483448..fd92878
> --- a/drivers/media/dvb-frontends/tda18271c2dd.c
> +++ b/drivers/media/dvb-frontends/tda18271c2dd.c
> @@ -328,7 +328,7 @@ static int CalcMainPLL(struct tda_state *state, u32 freq)
>  
>  	OscFreq = (u64) freq * (u64) Div;
>  	OscFreq *= (u64) 16384;
> -	do_div(OscFreq, (u64)16000000);
> +	do_div(OscFreq, 16000000);
>  	MainDiv = OscFreq;
>  
>  	state->m_Regs[MPD] = PostDiv & 0x77;
> @@ -352,7 +352,7 @@ static int CalcCalPLL(struct tda_state *state, u32 freq)
>  	OscFreq = (u64)freq * (u64)Div;
>  	/* CalDiv = u32( OscFreq * 16384 / 16000000 ); */
>  	OscFreq *= (u64)16384;
> -	do_div(OscFreq, (u64)16000000);
> +	do_div(OscFreq, 16000000);
>  	CalDiv = OscFreq;
>  
>  	state->m_Regs[CPD] = PostDiv;

The changes here do not match with the subject line of this patch.
I think it is best to split this into two patches, one for each source.

Regards,

	Hans