From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:42836 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751431AbaHPMxt (ORCPT ); Sat, 16 Aug 2014 08:53:49 -0400 Message-ID: <53EF5457.5080808@iki.fi> Date: Sat, 16 Aug 2014 14:53:43 +0200 From: Antti Palosaari MIME-Version: 1.0 To: Mauro Carvalho Chehab , "nibble.max" CC: linux-media , "olli.salonen" Subject: Re: [PATCH] m88ts2022: fix high symbol rate transponders missing on 32bit platform. References: <201408161412275930052@gmail.com> <20140816093854.39be5017.m.chehab@samsung.com> In-Reply-To: <20140816093854.39be5017.m.chehab@samsung.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 08/16/2014 02:38 PM, Mauro Carvalho Chehab wrote: > Em Sat, 16 Aug 2014 14:12:32 +0800 > "nibble.max" escreveu: > >> The current m88ts2022 driver will miss the following high symbol rate transponders on Telstar 18 138.0. >> 12385 H 43200, >> 12690 H 43200, >> 12538 V 41250... >> the code for f_3db_hz will overflow for the high symbol rate. >> for example, symbol rate=41250 KS/s >> symbol_rate * 135UL = 5568750000(1 4BEC 61B0), the value is larger than unsigned int on 32bit platform. >> that makes the wrong result. >> Exchanging the div and mul position fixs it. >> >> Signed-off-by: Nibble Max >> --- >> drivers/media/tuners/m88ts2022.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/media/tuners/m88ts2022.c b/drivers/media/tuners/m88ts2022.c >> index 40c42de..65c8acc 100644 >> --- a/drivers/media/tuners/m88ts2022.c >> +++ b/drivers/media/tuners/m88ts2022.c >> @@ -314,7 +314,7 @@ static int m88ts2022_set_params(struct dvb_frontend *fe) >> div_min = gdiv28 * 78 / 100; >> div_max = clamp_val(div_max, 0U, 63U); >> >> - f_3db_hz = c->symbol_rate * 135UL / 200UL; >> + f_3db_hz = (c->symbol_rate / 200UL) * 135UL; > > Hmm... wouldn't this make worse for low symbol rates? > > IMHO, the better is to use a u64 instead, and do_div64(). > >> f_3db_hz += 2000000U + (frequency_offset_khz * 1000U); >> f_3db_hz = clamp(f_3db_hz, 7000000U, 40000000U); >> I will look that more carefully on end of next week, go through possible symbol rates and rounding errors. Maybe it should be something like that (didn't test any way, may not even compile): f_3db_hz = div_u64((u64) (c->symbol_rate * 135), 200); Antti -- http://palosaari.fi/