From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-lb0-f174.google.com ([209.85.217.174]:62672 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753459Ab2HLAWz (ORCPT ); Sat, 11 Aug 2012 20:22:55 -0400 Received: by lbbgj3 with SMTP id gj3so796017lbb.19 for ; Sat, 11 Aug 2012 17:22:54 -0700 (PDT) Message-ID: <5026F74F.5060606@iki.fi> Date: Sun, 12 Aug 2012 03:22:39 +0300 From: Antti Palosaari MIME-Version: 1.0 To: Mauro Carvalho Chehab , linux-media Subject: Q: c->bandwidth_hz = (c->symbol_rate * rolloff) / 100 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hellou I saw there is nowadays logic in dvb-frontend which calculates bandwidth_hz value in cache. Calculation formula seems to be correct. But that makes me wonder if that is wise as it gives occupied bandwidth instead of nominal. For example I have typical DVB-C annex A, 8 MHz bandwidth, symbol rate 6875000 and roll-off factor 0.15. That gives calculation result is 7 906 250 Hz for nominal 8 000 000 Hz channel. This value is used only by tuner. Only visible effect is thus every tuner driver should use if statement to compare to find out nominal value as tuner chips usually configures low-pass filter steps of 8/7/6/5 MHz. For me it sounds better if tuner just gets nominal bandwidth - maybe calculating real used bw could be nice too as it is possible to return userspace. Shortly: I see it better to give nominal RF channel value for tuner. regards Antti -- http://palosaari.fi/