Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757146Ab0BKUvo (ORCPT ); Thu, 11 Feb 2010 15:51:44 -0500 Received: from mail-iw0-f195.google.com ([209.85.223.195]:43288 "EHLO mail-iw0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757128Ab0BKUvl (ORCPT ); Thu, 11 Feb 2010 15:51:41 -0500 Message-ID: <4B746DEC.7080602@billgatliff.com> Date: Thu, 11 Feb 2010 14:51:56 -0600 From: Bill Gatliff User-Agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090707) MIME-Version: 1.0 To: Pavel Machek CC: linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PWM PATCH 1/5] API to consolidate PWM devices behind a common user and kernel interface References: <20100211200456.GA1487@ucw.cz> In-Reply-To: <20100211200456.GA1487@ucw.cz> X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2102 Lines: 61 Pavel Machek wrote: > Exactly; if your hw can be damaged by software, it was misdesigned. > > Is the paragraph #1 really neccessary? > It provides a little background on the subject matter. I don't think it's mandatory, but I don't see the harm in keeping it. I think it improves the document overall from an editorial perspective, however. >> +pwm_free() -- Marks a PWM channel as no longer in use. The PWM device >> +is stopped before it is released by the API. >> > > free is normally used for something else. Rename to open/close? > ... or request/release? >> +pwm_start(), pwm_stop() -- Turns the PWM signal on and off. Except >> +where stated otherwise by a driver author, signals are stopped at the >> +end of the current period, at which time the output is set to its >> +inactive state. >> > > What does it mean to stop a signal? What is the difference between 0% > duty cycle and stop() ? > Depends on the hardware. For a true PWM peripheral, a 0% duty cycle might still have the base peripheral clock for the device running. Whereas a pwm_stop() signal could be used to turn off the clock to the peripheral. > Is polarity realy required? Can't driver just replace duty with > 100%-duty Actually, yes in some cases. Users can always do the 100%-duty math, but some hardware asserts a specific output state when you stop the peripheral that's potentially different from 0% duty. Also, some hardware begins the PWM cycle with the output high, while others do with the output low. It isn't necessarily the case that the user cares, but I was thinking that having the API allow for different polarity might prevent some applications having to optionally do the %duty vs. 100-%duty conversion themselves. b.g. -- Bill Gatliff Embedded systems training and consulting http://billgatliff.com bgat@billgatliff.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/