Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751652AbdGZMme (ORCPT ); Wed, 26 Jul 2017 08:42:34 -0400 Received: from hermes.aosc.io ([199.195.250.187]:34194 "EHLO hermes.aosc.io" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751474AbdGZMmc (ORCPT ); Wed, 26 Jul 2017 08:42:32 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Wed, 26 Jul 2017 20:42:23 +0800 From: icenowy@aosc.io To: Maxime Ripard Cc: =?UTF-8?Q?Ond=C5=99ej_Jirman?= , devicetree , "open list:THERMAL" , linux-sunxi , linux-kernel , Liam Girdwood , wens@csie.org, Mark Brown , linux-clk , linux-arm-kernel Subject: Re: [linux-sunxi] [PATCH 10/10] ARM: dts: sun8i: Add SY8106A regulator to Orange Pi PC In-Reply-To: <20170726114420.ipirqgbluqmggcjy@flea> References: <20170723102749.17323-1-icenowy@aosc.io> <20170723102749.17323-11-icenowy@aosc.io> <25C8A89C-8495-4787-934C-8E9667CD70BF@aosc.io> <82507f40a1ddba8517cf09f51d3afa33@aosc.io> <1501064628.14577.1.camel@megous.com> <20170726114420.ipirqgbluqmggcjy@flea> Message-ID: <5d25fc45c7beb2e3958f16fd741f0620@aosc.io> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2008 Lines: 56 在 2017-07-26 19:44，Maxime Ripard 写道： > Hi, > > On Wed, Jul 26, 2017 at 12:23:48PM +0200, Ondřej Jirman wrote: >> Hi, >> >> icenowy@aosc.io píše v St 26. 07. 2017 v 15:36 +0800: >> > >> > > > > >> > > > > Otherwse >> > > > > >> > > > > > + regulator-max-microvolt = <1400000>; >> > > > > > + regulator-ramp-delay = <200>; >> > > > > >> > > > > Is this an actual constraint of the SoC? Or is it a characteristic >> > > > > of the regulator? If it is the latter, it belongs in the driver. >> > > > > AFAIK the regulator supports varying the ramp delay (slew rate). >> > >> > I don't know... >> > >> > Maybe I should ask Ondrej? >> >> It is probably neither. >> >> It is used to calculate a delay inserted by the kernel between setting >> a new target voltage over I2C and changing the frequency of the CPU. >> The actual delay is calculated by the difference between previous and >> the new voltage. >> >> I don't remember seeing anything in the datasheet of the regulator. >> This is just some low value that works. >> >> It would probably be dependent on the capacitance on the output of the >> regulator, actual load (which varies), etc. So it is a board specific >> value. One could measure it with an oscilloscope if there's a need to >> optimize this. > > If this is a reasonable default, then this should be in the > driver. You can't expect anyone to properly calculate a ramp delay and > have access to both a scope and the CPU power lines. It seems that in regulator_desc structure a default value of ramp delay can be set, and the ones specified in dt can override it. So just add .ramp_delay = 200 in the driver's regulator_desc part? Should a comment be added that explains it's only an experienced value on Allwinner H3/H5 boards VDD-CPUX usage? > > Maxime > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel