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=-6.7 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 1346EC7618B for ; Mon, 29 Jul 2019 16:17:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2B822067D for ; Mon, 29 Jul 2019 16:17:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728363AbfG2QRA convert rfc822-to-8bit (ORCPT ); Mon, 29 Jul 2019 12:17:00 -0400 Received: from mailoutvs18.siol.net ([185.57.226.209]:60067 "EHLO mail.siol.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727408AbfG2QRA (ORCPT ); Mon, 29 Jul 2019 12:17:00 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.siol.net (Postfix) with ESMTP id CB4C9522935; Mon, 29 Jul 2019 18:16:56 +0200 (CEST) X-Virus-Scanned: amavisd-new at psrvmta10.zcs-production.pri Received: from mail.siol.net ([127.0.0.1]) by localhost (psrvmta10.zcs-production.pri [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id pA7Ggt9CdWmA; Mon, 29 Jul 2019 18:16:56 +0200 (CEST) Received: from mail.siol.net (localhost [127.0.0.1]) by mail.siol.net (Postfix) with ESMTPS id 4B0915225A6; Mon, 29 Jul 2019 18:16:56 +0200 (CEST) Received: from jernej-laptop.localnet (cpe-194-152-11-237.cable.triera.net [194.152.11.237]) (Authenticated sender: jernej.skrabec@siol.net) by mail.siol.net (Postfix) with ESMTPA id C909752294C; Mon, 29 Jul 2019 18:16:55 +0200 (CEST) From: Jernej =?utf-8?B?xaBrcmFiZWM=?= To: Uwe =?ISO-8859-1?Q?Kleine=2DK=F6nig?= Cc: thierry.reding@gmail.com, mripard@kernel.org, wens@csie.org, robh+dt@kernel.org, mark.rutland@arm.com, linux-pwm@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com Subject: Re: [PATCH 5/6] pwm: sun4i: Add support to output source clock directly Date: Mon, 29 Jul 2019 18:16:55 +0200 Message-ID: <2499807.IN78SsLMYo@jernej-laptop> In-Reply-To: <20190729070605.vlu7kgzn362ph2q3@pengutronix.de> References: <20190726184045.14669-1-jernej.skrabec@siol.net> <20190726184045.14669-6-jernej.skrabec@siol.net> <20190729070605.vlu7kgzn362ph2q3@pengutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Uwe, Dne ponedeljek, 29. julij 2019 ob 09:06:05 CEST je Uwe Kleine-König napisal(a): > On Fri, Jul 26, 2019 at 08:40:44PM +0200, Jernej Skrabec wrote: > > PWM core has an option to bypass whole logic and output unchanged source > > clock as PWM output. This is achieved by enabling bypass bit. > > > > Note that when bypass is enabled, no other setting has any meaning, not > > even enable bit. > > > > This mode of operation is needed to achieve high enough frequency to > > serve as clock source for AC200 chip, which is integrated into same > > package as H6 SoC. > > > > Signed-off-by: Jernej Skrabec > > --- > > > > drivers/pwm/pwm-sun4i.c | 31 ++++++++++++++++++++++++++++++- > > 1 file changed, 30 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c > > index 9e0eca79ff88..848cff26f385 100644 > > --- a/drivers/pwm/pwm-sun4i.c > > +++ b/drivers/pwm/pwm-sun4i.c > > @@ -120,6 +120,19 @@ static void sun4i_pwm_get_state(struct pwm_chip > > *chip, > > > > val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG); > > > > + /* > > + * PWM chapter in H6 manual has a diagram which explains that if bypass > > + * bit is set, no other setting has any meaning. Even more, experiment > > + * proved that also enable bit is ignored in this case. > > + */ > > + if (val & BIT_CH(PWM_BYPASS, pwm->hwpwm)) { > > + state->period = DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC, clk_rate); > > + state->duty_cycle = state->period / 2; > > + state->polarity = PWM_POLARITY_NORMAL; > > + state->enabled = true; > > + return; > > + } > > + > > > > if ((PWM_REG_PRESCAL(val, pwm->hwpwm) == PWM_PRESCAL_MASK) && > > > > sun4i_pwm->data->has_prescaler_bypass) > > > > prescaler = 1; > > > > @@ -211,7 +224,8 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, > > struct pwm_device *pwm,> > > { > > > > struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip); > > struct pwm_state cstate; > > > > - u32 ctrl; > > + u32 ctrl, clk_rate; > > + bool bypass; > > > > int ret; > > unsigned int delay_us; > > unsigned long now; > > > > @@ -226,6 +240,16 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, > > struct pwm_device *pwm,> > > } > > > > } > > > > + /* > > + * Although it would make much more sense to check for bypass in > > + * sun4i_pwm_calculate(), value of bypass bit also depends on "enabled". > > + * Period is allowed to be rounded up or down. > > + */ > > Every driver seems to implement rounding the way its driver considers it > sensible. @Thierry: This is another patch where it would be good to have > a global directive about how rounding is supposed to work to provide the > users an reliable and uniform way to work with PWMs. > > > + clk_rate = clk_get_rate(sun4i_pwm->clk); > > + bypass = (state->period == NSEC_PER_SEC / clk_rate || > > + state->period == DIV_ROUND_UP(NSEC_PER_SEC, clk_rate)) && > > + state->enabled; > > Not sure if the compiler is clever enough to notice the obvious > optimisation with this code construct, but you can write this test in a > more clever way which has zero instead of up to two divisions. Something > like: > > bypass = ((state->period * clk_rate >= NSEC_PER_SEC && > state->period * clk_rate < NSEC_PER_SEC + clk_rate) && > state->enabled); > > In the commit log you write the motivation for using bypass is that it > allows to implement higher frequency then with the "normal" operation. > As you don't skip calculating the normal parameters requesting such a > high-frequency setting either errors out or doesn't catch the impossible > request. In both cases there is something to fix. It's the latter, otherwise it wouldn't work for my case. I'll fix the check and skip additional logic. > > > + > > > > spin_lock(&sun4i_pwm->ctrl_lock); > > ctrl = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG); > > > > @@ -273,6 +297,11 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, > > struct pwm_device *pwm,> > > ctrl &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm); > > > > } > > > > + if (bypass) > > + ctrl |= BIT_CH(PWM_BYPASS, pwm->hwpwm); > > + else > > + ctrl &= ~BIT_CH(PWM_BYPASS, pwm->hwpwm); > > + > > Does switching on (or off) the bypass bit complete the currently running > period? I don't really know. If I understand correctly, it just bypasses PWM logic completely, so I would say it doesn't complete the currently running period. Take a look at chapter 3.9.2 http://linux-sunxi.org/ File:Allwinner_H6_V200_User_Manual_V1.1.pdf Best regards, Jernej > > > sun4i_pwm_writel(sun4i_pwm, ctrl, PWM_CTRL_REG); > > > > spin_unlock(&sun4i_pwm->ctrl_lock); > > Best regards > Uwe