From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24F0FC1975A for ; Thu, 12 Mar 2020 06:40:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20358206F7 for ; Thu, 12 Mar 2020 06:40:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387942AbgCLGks (ORCPT ); Thu, 12 Mar 2020 02:40:48 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:35201 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387859AbgCLGkr (ORCPT ); Thu, 12 Mar 2020 02:40:47 -0400 Received: from pty.hi.pengutronix.de ([2001:67c:670:100:1d::c5]) by metis.ext.pengutronix.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jCHWN-0008Mo-GT; Thu, 12 Mar 2020 07:40:43 +0100 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1jCHWN-0003bp-0t; Thu, 12 Mar 2020 07:40:43 +0100 Date: Thu, 12 Mar 2020 07:40:42 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Lokesh Vutla Cc: Thierry Reding , Tony Lindgren , Linux OMAP Mailing List , linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, Sekhar Nori , Vignesh R Subject: Re: [PATCH v3 4/5] pwm: omap-dmtimer: Do not disable pwm before changing period/duty_cycle Message-ID: <20200312064042.p7himm3odxjyzroi@pengutronix.de> References: <20200312042210.17344-1-lokeshvutla@ti.com> <20200312042210.17344-5-lokeshvutla@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200312042210.17344-5-lokeshvutla@ti.com> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c5 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 12, 2020 at 09:52:09AM +0530, Lokesh Vutla wrote: > Only the Timer control register(TCLR) cannot be updated when the timer > is running. Registers like Counter register(TCRR), loader register(TLDR), > match register(TMAR) can be updated when the counter is running. Since > TCLR is not updated in pwm_omap_dmtimer_config(), do not stop the > timer for period/duty_cycle update. I'm not sure what is sensible here. Stopping the PWM for a short period is bad, but maybe emitting a wrong period isn't better. You can however optimise it if only one of period or duty_cycle changes. @Thierry, what is your position here? I tend to say a short stop is preferable. > Tested-by: Tony Lindgren > Signed-off-by: Lokesh Vutla > --- > drivers/pwm/pwm-omap-dmtimer.c | 21 +++++++-------------- > 1 file changed, 7 insertions(+), 14 deletions(-) > > diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c > index 85b17b49980b..c56e7256e923 100644 > --- a/drivers/pwm/pwm-omap-dmtimer.c > +++ b/drivers/pwm/pwm-omap-dmtimer.c > @@ -19,6 +19,13 @@ > * Limitations: > * - When PWM is stopped, timer counter gets stopped immediately. This > * doesn't allow the current PWM period to complete and stops abruptly. > + * - When PWM is running and changing both duty cycle and period, > + * we cannot prevent in software that the output might produce > + * a period with mixed settings. Especially when period/duty_cyle > + * is updated while the pwm pin is high, current pwm period/duty_cycle > + * can get updated as below based on the current timer counter: > + * - period for current cycle = current_period + new period > + * - duty_cycle for current period = current period + new duty_cycle. In case we stay with a short stop, adding something like: - The PWM has to be stopped for updates of both period and duty_cycle. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |