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=-3.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 4C44CC43331 for ; Wed, 1 Apr 2020 16:52:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E5B92063A for ; Wed, 1 Apr 2020 16:52:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=pqgruber.com header.i=@pqgruber.com header.b="ugZWMCya" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733054AbgDAQv7 (ORCPT ); Wed, 1 Apr 2020 12:51:59 -0400 Received: from mail.pqgruber.com ([52.59.78.55]:57474 "EHLO mail.pqgruber.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388555AbgDAQgo (ORCPT ); Wed, 1 Apr 2020 12:36:44 -0400 Received: from workstation.tuxnet (213-47-165-233.cable.dynamic.surfer.at [213.47.165.233]) by mail.pqgruber.com (Postfix) with ESMTPSA id C530EC425A3; Wed, 1 Apr 2020 18:36:41 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pqgruber.com; s=mail; t=1585759002; bh=IPYAP+Th3gWr6c1GcWqNIip3jHxnwVBTe6y78MvI8lk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ugZWMCyav4coGCw7rKKWrZ9FiyO4+kuMLcOtv4VI+dX6Ydn8s6iUO/XwnBHf9iBW7 0ZpFzHUamm3Ku5foVMNFg4SZOHqzxnK7n+KcwmIRZFzBRHw2CCtMGFAs3+8DHwACGl btyHxOyEQhQSKy+IH63DzU4cwLr8YFpWW7ENiLYk= Date: Wed, 1 Apr 2020 18:36:40 +0200 From: Clemens Gruber To: Thierry Reding Cc: Andy Shevchenko , Matthias Schiffer , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , linux-pwm@vger.kernel.org, Linux Kernel Mailing List , Sven Van Asbroeck Subject: Re: [PATCH 1/4] pwm: pca9685: remove unused duty_cycle struct element Message-ID: <20200401163640.GA91358@workstation.tuxnet> References: <20200226135229.24929-1-matthias.schiffer@ew.tq-group.com> <20200330130743.GB2431644@ulmo> <20200330160238.GD2817345@ulmo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200330160238.GD2817345@ulmo> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 30, 2020 at 06:02:38PM +0200, Thierry Reding wrote: > On Mon, Mar 30, 2020 at 04:18:22PM +0300, Andy Shevchenko wrote: > > On Mon, Mar 30, 2020 at 4:09 PM Thierry Reding wrote: > > > > > > On Wed, Feb 26, 2020 at 02:52:26PM +0100, Matthias Schiffer wrote: > > > > duty_cycle was only set, never read. > > > > > > > > Signed-off-by: Matthias Schiffer > > > > --- > > > > drivers/pwm/pwm-pca9685.c | 4 ---- > > > > 1 file changed, 4 deletions(-) > > > > > > Applied, thanks. > > > > I'm not sure this patch is correct. > > What makes you say that? If you look at the code, the driver sets this > field to either 0 or some duty cycle value but ends up never using it. > Why would it be wrong to remove that code? > > > We already have broken GPIO in this driver. Do we need more breakage? > > My understanding is that nobody was able to pinpoint exactly when this > regressed, or if this only worked by accident to begin with. It sounds > like Clemens has a way of testing this driver, so perhaps we can solve > that GPIO issue while we're at it. > > The last discussion on this seems to have been around the time when you > posted a fix for it: > > https://patchwork.ozlabs.org/patch/1156012/ > > But then Sven had concerns that that also wasn't guaranteed to work: > > https://lkml.org/lkml/2019/6/2/73 > > So I think we could either apply your patch to restore the old behaviour > which I assume you tested, so at least it seems to work in practice, > even if there's still a potential race that Sven pointed out in the > above link. > > I'd prefer something alternative because it's obviously confusing and > completely undocumented. Mika had already proposed something that's a > little bit better, though still somewhat confusing. > > Oh... actually reading further through those threads there seems to be a > patch from Sven that was reviewed by Mika but then nothing happened: > > https://lkml.org/lkml/2019/6/4/1039 > > with the corresponding patchwork URL: > > https://patchwork.ozlabs.org/patch/1110083/ > > Andy, Clemens, do you have a way of testing the GPIO functionality of > this driver? If so, it'd be great if you could check the above patch > from Sven to fix PWM/GPIO interop. Looks good. Tested it today and I can no longer reproduce the issues when switching between PWM and GPIO modes. It did not apply cleanly on the current mainline or for-next branch, so I'll send a fixed up version of the patch with my Tested-by tag shortly. I noticed an unrelated issue when disabling and enabling the channel though, for which I will either send a patch or maybe try to convert the driver to the atomic API first and then look if it is still a problem. (Issue is that if you disable the channel, the LED_OFF counter is cleared, which means you have to reconfigure the duty cycle after reenabling. It's probably better if only the FULL_OFF bit is toggled in enable/disable as it has precedence over the others anyway and then the previous state would not be changed..?) Clemens