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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 06B0EC0044D for ; Mon, 16 Mar 2020 07:26:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA3F620663 for ; Mon, 16 Mar 2020 07:26:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729945AbgCPH0Y (ORCPT ); Mon, 16 Mar 2020 03:26:24 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:57451 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729554AbgCPH0Y (ORCPT ); Mon, 16 Mar 2020 03:26:24 -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 1jDk8e-0006VD-7S; Mon, 16 Mar 2020 08:26:16 +0100 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1jDk8b-0003K3-GS; Mon, 16 Mar 2020 08:26:13 +0100 Date: Mon, 16 Mar 2020 08:26:13 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Pascal Roeleven Cc: Thierry Reding , Maxime Ripard , Chen-Yu Tsai , Philipp Zabel , linux-pwm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com Subject: Re: pwm: sun4i: pwm-backlight not working since 5.6-rc1 Message-ID: <20200316072613.37lnjfloac4npudf@pengutronix.de> References: <6185b5540ca082d887d7d13330c9d938@pascalroeleven.nl> <20200312132942.2kfspvmoc3mxkdx4@pengutronix.de> <6e995c4c22c4e6c93acb1f491e5aa109@pascalroeleven.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6e995c4c22c4e6c93acb1f491e5aa109@pascalroeleven.nl> 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 Hello, On Thu, Mar 12, 2020 at 04:06:07PM +0100, Pascal Roeleven wrote: > On 2020-03-12 14:29, Uwe Kleine-König wrote: > > On Thu, Mar 12, 2020 at 01:22:13PM +0100, Pascal Roeleven wrote: > > > Hi all, > > > > > > I am working on adding an old A10 device to mainline and noticed an > > > issue > > > when testing on 5.5.8 vs master. > > > > > > Since 5.6-rc1, I can't control the brightness of my LCD backlight > > > anymore. > > > The backlight stays on full brightness instead. I am controlling the > > > brightness value via sysfs for testing. > > > > > > I am not sure if this is a general pwm-sun4i issue or if it is > > > related to > > > the backlight. However I narrowed it down to one commit for pwm-sun4i: > > > > > > fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 > > > > > > If I use pwm-sun4i.c from 5b090b430d750961305030232314b6acdb0102aa on > > > master, the backlight works fine. Unfortunately, due to my lack of > > > kernel > > > experience, I can't see how the commit above broke it. > > > > Hmm, I cannot see how fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 breaks > > this. Looking at the output of > > > > git show -b fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 > > > > (i.e. ignoring whitespace changes) I don't see how the behaviour you're > > reporting can be explained. > > > > Are you sure that fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 is the bad > > commit? > > > > Can you install a tool to inspect register values and check how the > > affected registers change if you switch kernel versions and/or pwm > > settings? > > > > (e.g. > > memtool md 0x1c20e00+0xc > > ) > > > > Best regards > > Uwe > > Thanks for your response. > > Yes I am sure that is the commit. If I am on master, and replace pwm-sun4i.c > with the one from 5b090b43, everything works. If I then apply fa4d8178, it > stops working. > > And strangely the output of the registers is exactly the same before and > after fa4d8178: > > 01c20e00: 00000050 00130014 00000000 (full brightness) > 01c20e00: 00000050 00130006 00000000 (min brightness) > > Even when I'm on 5b090b43 and cherry-pick fa4d8178 can I reproduce the > issue. Very strange. I'm out of sensible ideas. The remaining ones are: - enable tracing in the kernel and boot with trace_event=pwm And then check after the problem occurred in /sys/kernel/debug/tracing/trace if something sticks out. - Try modifying the registers using memtool. E.g. memtool mw 0x01c20e04 0x00130012 - Do you have equipment to check the actual output of the PWM hardware? If so, what do you see? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |