linux-kernel - Re: [PATCH v5 1/6] media: dvb-frontends: tda10048: Make the range of z explicit.

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Message-ID: <CANiDSCt900xLuroAkBhkpVDrz9Y9Eixdn544=uYZd6RnB2Ve3w@mail.gmail.com>
Date: Tue, 7 Jan 2025 22:26:27 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Kosta Stefanov <costa.stephanoff@...il.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, Stanimir Varbanov <stanimir.k.varbanov@...il.com>, 
	Vikash Garodia <quic_vgarodia@...cinc.com>, "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>, 
	Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v5 1/6] media: dvb-frontends: tda10048: Make the range of
 z explicit.

Thanks Kosta!

On Tue, 7 Jan 2025 at 18:28, Kosta Stefanov <costa.stephanoff@...il.com> wrote:
>
> hi Ricardo, according to the datasheet the recommended sampling
> frequency is 55 MHz (BTW, if you look at the definitions in the source
> code and make the calculations that is exactly the sampling frequency
> all currently supported in Linux devices are using as well).
>
> also, I spent few minutes time to make the calculations based on the
> restrains of the PLL build-in tda10048 and in theory the maximum is 69
> MHz. so, if you make next revision of this patch, feel free to update
> the comment accordingly, in short - recommended sampling frequency of
> 55 MHz, theoretical maximum of 69 MHz.
>
> in any case, your assumption is correct and in reality is away less
> than the maximum value you assumed.

I have updated the comments in my local copy. I will resend after a
couple of days in case there are more reviews.

May I ask if you could share the datasheet?

Thanks!

>
> Reviewed-by: Kosta Stefanov <costa.stephanoff@...il.com>
>
> --Kosta
>
>
> On Tue, Jan 7, 2025 at 12:54 PM Ricardo Ribalda <ribalda@...omium.org> wrote:
> >
> > We have not been able to find the relevant datahsheet, but it seems rare
> > that the device will have a sampling frequency over 613MHz.
> >
> > Nonetheless, this patch does not introduce any change in behaviour, it
> > just adds a comment to make explicit the current limit: div by 32 bits.
> >
> > 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 */
> >         z = 7 * sample_freq_hz;
> >         do_div(t, z);
> >         t += 5;
> >
> > --
> > 2.47.1.613.gc27f4b7a9f-goog
> >
> >



-- 
Ricardo Ribalda