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

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Date: Fri, 03 May 2024 16:08:48 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Dan Carpenter <dan.carpenter@...aro.org>, Mauro Carvalho Chehab
 <mchehab@...nel.org>, Martin Tuma <martin.tuma@...iteqautomotive.com>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>, Hugues Fruchet
 <hugues.fruchet@...s.st.com>, Alain Volmat <alain.volmat@...s.st.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue
 <alexandre.torgue@...s.st.com>, Paul Kocialkowski
 <paul.kocialkowski@...tlin.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec
 <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, Sakari
 Ailus <sakari.ailus@...ux.intel.com>, Thierry Reding
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 Bryan O'Donoghue <bryan.odonoghue@...aro.org>, Bjorn Andersson
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 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v3 26/26] media: dvb-frontends: tda10048: Make the range
 of z explicit.

Hello Ricardo,

On 2024-05-03 13:56, Ricardo Ribalda wrote:
> I am trying to get the DS, but
> https://www.nxp.com/acrobat_download/literature/9397/75015931.pdf is a
> dead links now.
> 
> Anyone have access to the datasheet?

It's kind of available on the link below, but for some strange reason
the download fails after downloading the first 128 KB or so.

https://web.archive.org/web/20080907185532/https://www.nxp.com/acrobat_download/literature/9397/75015931.pdf

> On Fri, 3 May 2024 at 13:55, Dan Carpenter <dan.carpenter@...aro.org> 
> wrote:
>> 
>> On Fri, May 03, 2024 at 11:27:58AM +0100, Mauro Carvalho Chehab wrote:
>> > 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.
>> 
>> This patch preserves the existing behavior. The sample_freq_hz 
>> variable
>> is a u32 so, in the original code, z couldn't have been more than
>> U32_MAX even though it was declared as a u64.
>> 
>> It's possible that the original code was wrong.  We have seen that in
>> other places in this patchset.  Adding a note about the datasheet is
>> also a good idea.
>> 
>> regards,
>> dan carpenter
>>