From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:43900 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751630Ab2GGKrF (ORCPT ); Sat, 7 Jul 2012 06:47:05 -0400 Message-ID: <4FF8139F.7010602@iki.fi> Date: Sat, 07 Jul 2012 13:46:55 +0300 From: Antti Palosaari MIME-Version: 1.0 To: Mauro Carvalho Chehab CC: Bert Massop , linux-media@vger.kernel.org Subject: Re: [PATCH 3/3] [media] tuner, xc2028: add support for get_afc() References: <1341497792-6066-1-git-send-email-mchehab@redhat.com> <1341497792-6066-3-git-send-email-mchehab@redhat.com> <4FF5AD40.3070707@iki.fi> <4FF5F4C4.7080904@redhat.com> In-Reply-To: <4FF5F4C4.7080904@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 07/05/2012 11:10 PM, Mauro Carvalho Chehab wrote: > Em 05-07-2012 14:37, Bert Massop escreveu: >> On Thu, Jul 5, 2012 at 5:05 PM, Antti Palosaari wrote: >>> >>> On 07/05/2012 05:16 PM, Mauro Carvalho Chehab wrote: >>>> >>>> Implement API support to return AFC frequency shift, as this device >>>> supports it. The only other driver that implements it is tda9887, >>>> and the frequency there is reported in Hz. So, use Hz also for this >>>> tuner. >>> >>> >>> What is AFC and why it is needed? >>> >> >> AFC is short for Automatic Frequency Control, by which a tuner >> automatically fine-tunes the frequency for the best reception, >> compensating for small offsets and oscillator frequency drift. >> This is however done automatically on the tuner, so its configuration >> is read-only. Aside from being a "nice to know" statistic, getting >> hold of the AFC frequency shift does as far as I know not have any >> practical uses related to properly operating the tuner. > > AFC might be useful on a few situations. For example, my CATV operator > still broadcasts some channels in both analog and digital. The analog > equipment there doesn't seem to be well-maintained, as some channels have > frequency shifts or have some other artifacts. Still, analog broadcast > is useful for me to test drivers ;) > > Anyway, adjusting the channel tables to consider that offset shift help > to tune them a little faster and/or get a better quality by letting the > PLL to work closer to the pilot carrier. We has already .get_frequency() which returns same information. It is not currently used though few drivers implements it (wrongly). So I don't see why this new callback should be added. u32 actual_freq; int afc; struct dtv_frontend_properties *c = &fe->dtv_property_cache; ret = .get_frequency(fe, &actual_freq); afc = c->frequency - actual_freq; regards Antti -- http://palosaari.fi/