From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752061AbeBAJui (ORCPT ); Thu, 1 Feb 2018 04:50:38 -0500 Received: from esa5.microchip.iphmx.com ([216.71.150.166]:10075 "EHLO esa5.microchip.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751628AbeBAJue (ORCPT ); Thu, 1 Feb 2018 04:50:34 -0500 X-IronPort-AV: E=Sophos;i="5.46,443,1511852400"; d="scan'208";a="8780226" Date: Thu, 1 Feb 2018 10:50:21 +0100 From: Ludovic Desroches To: Rob Herring CC: Linus Walleij , Ludovic Desroches , Linux ARM , , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Nicolas Ferre , Alexandre Belloni , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] pinctrl: at91-pio4: add support for drive-strength property Message-ID: <20180201095021.GA2580@rfolt0960.corp.atmel.com> Mail-Followup-To: Rob Herring , Linus Walleij , Linux ARM , linux-gpio@vger.kernel.org, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Nicolas Ferre , Alexandre Belloni , "linux-kernel@vger.kernel.org" References: <20180118160208.16461-1-ludovic.desroches@microchip.com> <20180129190130.qjej6hmudszzbfdz@rob-hp-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20180129190130.qjej6hmudszzbfdz@rob-hp-laptop> User-Agent: Mutt/1.9.3 (2018-01-21) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 29, 2018 at 01:01:30PM -0600, Rob Herring wrote: > On Mon, Jan 22, 2018 at 09:37:38AM +0100, Linus Walleij wrote: > > On Thu, Jan 18, 2018 at 5:02 PM, Ludovic Desroches > > wrote: > > > > > Add support for the drive-strength property. Usually its value is > > > expressed in mA. Since the numeric value depends on VDDIOP voltage, > > > the controller uses low, medium and high to define the drive-strengh. > > > > Aha I see. That's complex. It certainly results in a certain mA drive > > strength in the end, but what you're saying is that this is not usually > > what we configure. > > > > > The PIO controller accepts two values for the low drive: 0 or 1. Most > > > of the time, we don't care about the drive strength, there is no need > > > to change it, so 0 is considered as the default value. > > > > Do you mean default value as in "whatever the hardware was set > > up as at boot time"? > > > > > The low-drive > > > value won't be advertised through pinconf-pins file excepted if it > > > > except? > > > > > has been set explicitly in the device tree ie if its value is > > > different from 0. > > > > > > Signed-off-by: Ludovic Desroches > > > > OK I think I get it. > > > > > Optional properties: > > > - GENERIC_PINCONFIG: generic pinconfig options to use, bias-disable, > > > -bias-pull-down, bias-pull-up, drive-open-drain, input-schmitt-enable, > > > -input-debounce, output-low, output-high. > > > +bias-pull-down, bias-pull-up, drive-open-drain, drive-strength, > > > +input-schmitt-enable, input-debounce, output-low, output-high. > > (...) > > > + drive-strength = ; > > > > So you say you support this argument and it will be something like > > > > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_LO 1 > > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_ME 2 > > include/dt-bindings/pinctrl/at91.h:#define ATMEL_PIO_DRVSTR_HI 3 > > > > But the definition if generic drive strength is actually in mA. > > Yes, and the reason we put unit suffixes on properties is to avoid > differing units. > > > I think it is OK to deviate from stating it in mA, but you should > > write this in the DT bindings so people do not get confused. > > I don't think it is okay. If "drive-strength" doesn't work, then use > a vendor specific property ("atmel,drive-strength"). Of course, I might > forget this in the next version and tell you to use a standard property > in mA. Ok, so I am going to send the next version! The purpose is to keep using the generic pinconf parsing function. If I need to use "atmel,drive-strength" property, I assume I could manage it with custom_params, isn't it? Regards Ludovic