From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751023AbdE3TFV (ORCPT ); Tue, 30 May 2017 15:05:21 -0400 Received: from mout.kundenserver.de ([212.227.17.10]:64045 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750885AbdE3TFU (ORCPT ); Tue, 30 May 2017 15:05:20 -0400 Date: Tue, 30 May 2017 21:04:41 +0200 (CEST) From: Stefan Wahren To: Phil Elwell , linux-clk@vger.kernel.org, Eric Anholt , linux-kernel@vger.kernel.org, Michael Turquette , Stephen Boyd , Florian Fainelli , linux-rpi-kernel@lists.infradead.org Message-ID: <1412052002.45738.1496171081779@email.1und1.de> In-Reply-To: References: Subject: Re: [PATCH 2/2] clk: bcm2835: Minimise clock jitter for PCM clock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Medium X-Mailer: Open-Xchange Mailer v7.8.2-Rev34 X-Originating-Client: open-xchange-appsuite X-Provags-ID: V03:K0:cJYWuoEWS9VMELOX8pwsJPkYN4uU4cuEOGSL/FXO3nuGWtci2qr Bw7KupCIkZWUnKEiRi/13d2SmQIqV0JShO9mtACsdsk3gO7jZMkRpMwMz7MqUc54bgQ8rqp ExuswHdt3FxMId1FY1XL6nA+q/N3OtM6L3Uz42s78Qbf1KOR9yDE5iIX2F2NWZih9v1vhH9 jh2kh6ItXYwBX0oGvrwCw== X-UI-Out-Filterresults: notjunk:1;V01:K0:lLf59uYIg04=:+Pz6VcLK0bRLyuHGPE1Agx CEjpYMadv9WpS713gzRHIkiXRBoLnonRM8TAymSeM53riX+1mcykmCBp7HQwjyqyo2pFTL4ju POranF0qhRD1RgJPvmZmhviOc4sI/CaBNgy7tP/khL0l8t0kyUbo2JNus2L46eFcGbRVxXy3L +LqrEQ4kkVWxrHXz8UTskGnqPDWe2M91IwzbHCN9fpP7R4QZw1UebtIIos8j1OhvybLYlROwM Qcoii/grVFG9KRDM9kr/KKOAADYlSp9BZgObNMxcR9h1Mpse5cslb7hrc+ayyFNx/lk2WfH9T lyJpumllhqFwZp3d5JhLvrrKJGepPklrexZnxj1VsVaAKDQ1xyoLCzKWc0qK2wAefq0rblFCM qJyerbXbsn0/6AP1ZkDrA6xYAo0mGICUJqNACpti/72wZJVaPOihSEQUqiEegjfb1JE/SR1Jq CYx+/2MNhNlmDFpdSoBJiW8p71TJeLXlP739cCO/4n6Uwui/d3O52wYWGXBUgz+z8y5fLCXQL IDBFWOYcxrxyPt0/TcMbAGQAlqMdrnnO8zMGl1ugaWUbqqhFtDxHqiJp/pC4bf1FkpgAs3OtY F3SY/wiyiCLP7ttxfJy2VAOroE5o8JmNudkCxZwPR5SrRmkwHFyMDvIPMRcnFmizIxMbnLbrZ HnQJCIJVpf/4nGJXo31bEsM4mzBi/IWFEO0vz348qsry3AxttITOUinHcDdcHfNTs4Z2mKM6R 3QNCMEHHnlV9j5rD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Phil, > Phil Elwell hat am 30. Mai 2017 um 18:28 geschrieben: > > > Fractional clock dividers generate accurate average frequencies but > with jitter, particularly when the integer divisor is small. > > Introduce a new metric of clock accuracy to penalise clocks with a good > average but worse jitter compared to clocks with an average which is no > better but with lower jitter. The metric is the ideal rate minus the > worse deviation from that ideal using the nearest integer divisors. > > Use this metric for parent selection for clocks requiring low jitter > (currently just PCM). > > Signed-off-by: Phil Elwell > --- > drivers/clk/bcm/clk-bcm2835.c | 39 ++++++++++++++++++++++++++++++++++----- > 1 file changed, 34 insertions(+), 5 deletions(-) > > diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c > index facc346..e0ce5e7 100644 > --- a/drivers/clk/bcm/clk-bcm2835.c > +++ b/drivers/clk/bcm/clk-bcm2835.c > @@ -530,6 +530,7 @@ struct bcm2835_clock_data { > > bool is_vpu_clock; > bool is_mash_clock; > + bool low_jitter; > > u32 tcnt_mux; > }; > @@ -1124,7 +1125,8 @@ static unsigned long bcm2835_clock_choose_div_and_prate(struct clk_hw *hw, > int parent_idx, > unsigned long rate, > u32 *div, > - unsigned long *prate) > + unsigned long *prate, > + unsigned long *avgrate) > { > struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw); > struct bcm2835_cprman *cprman = clock->cprman; > @@ -1136,11 +1138,33 @@ static unsigned long bcm2835_clock_choose_div_and_prate(struct clk_hw *hw, > parent = clk_hw_get_parent_by_index(hw, parent_idx); > > if (!(BIT(parent_idx) & data->set_rate_parent)) { > + unsigned long tmp_rate; > + > *prate = clk_hw_get_rate(parent); > *div = bcm2835_clock_choose_div(hw, rate, *prate, true); > > - return bcm2835_clock_rate_from_divisor(clock, *prate, > - *div); > + tmp_rate = bcm2835_clock_rate_from_divisor(clock, *prate, *div); > + *avgrate = tmp_rate; > + > + if (data->low_jitter && (*div & CM_DIV_FRAC_MASK)) { > + unsigned long high, low; > + u32 idiv = *div & ~CM_DIV_FRAC_MASK; > + > + high = bcm2835_clock_rate_from_divisor(clock, *prate, > + idiv); > + idiv += CM_DIV_FRAC_MASK + 1; > + low = bcm2835_clock_rate_from_divisor(clock, *prate, > + idiv); What about int_div or intdiv instead of idiv as variable name? > + > + /* Return a value which is the maximum deviation > + * below the ideal rate, for use as a metric. > + */ Please fix coding style of the comment. Thanks Stefan