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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1826FC77B73 for ; Mon, 5 Jun 2023 07:16:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230145AbjFEHQQ (ORCPT ); Mon, 5 Jun 2023 03:16:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231187AbjFEHQL (ORCPT ); Mon, 5 Jun 2023 03:16:11 -0400 Received: from mx.sberdevices.ru (mx.sberdevices.ru [45.89.227.171]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7FBE4E51; Mon, 5 Jun 2023 00:15:46 -0700 (PDT) Received: from s-lin-edge02.sberdevices.ru (localhost [127.0.0.1]) by mx.sberdevices.ru (Postfix) with ESMTP id 6AB235FD15; Mon, 5 Jun 2023 10:15:25 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sberdevices.ru; s=mail; t=1685949325; bh=90SqCFueETbn6QtgfnNvoKqDRDdO5vsmVtd1isEyw1s=; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; b=otdrzu2Cj3M3qp/s9Um/15X1vMoT3/iSXKdEvCYUqRvTqI3PFPts5reMsTYQ9N+Q4 T/SyS/gyp5K2MnVz32iWqsW+Z6gla/2oLoZKbk942iXH7HrFybB8P55iwuWSVt3LD4 luvKpki5t5Ufikqr16gRj3XbyamywuLOK1KGVVe14UpqhdWR0K/kDte9mA1LWUByJP hRItvErnfdm6dsRG+jlfIrbIQOSBSIC0Gdqa4SSUXLatqCxcXRc6IzyyDpuwTnZVux 3cgDdH+4NP7EZg2Ir7xEG1IiHHpU77YLf0LI21TBaFW8G/zeyzf//X5/WHJKhhlN3t hggtgsSf5hotw== Received: from S-MS-EXCH01.sberdevices.ru (S-MS-EXCH01.sberdevices.ru [172.16.1.4]) by mx.sberdevices.ru (Postfix) with ESMTP; Mon, 5 Jun 2023 10:15:24 +0300 (MSK) Message-ID: Date: Mon, 5 Jun 2023 10:11:09 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH] pwm: meson: compute cnt register value in proper way Content-Language: en-US To: Heiner Kallweit CC: "thierry.reding@gmail.com" , "linux-iio@vger.kernel.org" , "u.kleine-koenig@pengutronix.de" , "neil.armstrong@linaro.org" , "martin.blumenstingl@googlemail.com" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-amlogic@lists.infradead.org" , kernel , Dmitry Rokosov , "jbrunet@baylibre.com" , "khilman@baylibre.com" References: <20230602103211.2199283-1-gnstark@sberdevices.ru> From: George Stark In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [172.16.1.6] X-ClientProxiedBy: S-MS-EXCH01.sberdevices.ru (172.16.1.4) To S-MS-EXCH01.sberdevices.ru (172.16.1.4) X-KSMG-Rule-ID: 4 X-KSMG-Message-Action: clean X-KSMG-AntiSpam-Status: not scanned, disabled by settings X-KSMG-AntiSpam-Interceptor-Info: not scanned X-KSMG-AntiPhishing: not scanned, disabled by settings X-KSMG-AntiVirus: Kaspersky Secure Mail Gateway, version 1.1.2.30, bases: 2023/06/05 04:52:00 #21434197 X-KSMG-AntiVirus-Status: Clean, skipped Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/2/23 23:52, Heiner Kallweit wrote: > On 02.06.2023 12:32, George Stark wrote: >> According to the datasheet, the PWM high and low clock count values >> should be set to at least one. Therefore, setting the clock count >> register to 0 actually means 1 clock count. >> >> Signed-off-by: George Stark >> Signed-off-by: Dmitry Rokosov >> --- >> This patch is based on currently unmerged patch by Heiner Kallweit >> https://lore.kernel.org/linux-amlogic/23fe625e-dc23-4db8-3dce-83167cd3b206@gmail.com >> --- >> diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c >> index 834acd7..57e7d9c 100644 >> --- a/drivers/pwm/pwm-meson.c >> +++ b/drivers/pwm/pwm-meson.c >> @@ -206,6 +206,11 @@ >> channel->pre_div = pre_div; >> channel->hi = duty_cnt; >> channel->lo = cnt - duty_cnt; >> + >> + if (channel->hi) >> + channel->hi--; >> + if (channel->lo) >> + channel->lo--; Hello Heiner Thanks for review > I'm not sure whether we should do this. duty_cnt and cnt are results > of an integer division and therefore potentially rounded down. > The chip-internal increment may help to compensate such rounding > errors, so to say. With the proposed change we may end up with the > effective period being shorter than the requested one. Although chip-internal increment sometimes may help accidentally there are cases when the increment ruins precise calculation in unexpected way. Here's our experience on meson a113l (meson-a1) with pwm driver based on ccf: we need to get pwm period as close as possible to 32768hz. config pwm to period 1/32768 = 30517ns, duty 15258n How driver calculates hi\lo regs: rate = NSEC_PER_SEC * 0xffff / 30517 = ~2147Mhz rate = clk_round_rate(rate) clk_round_rate selects fastest parent clock which is 64Mhz in our case then calculating hi\lo at last: period= mul_u64_u64_div_u64(rate, state->period, NSEC_PER_SEC); // 1953 duty= mul_u64_u64_div_u64(rate, state->duty_cycle, NSEC_PER_SEC); // 976 channel->hi= duty; channel->lo= period- duty; with the internal increment we'll have real output (1953-976 + 1 + 976 + 1) * 1 / 64Mhz = 32736.57Hz but we should have (1953-976 + 976) * 1 / 64Mhz = 32770.09Hz | And IIRC this should not happen. Could you please explain why or point out doc/description where it's stated? If so we can add explicit check to prevent such a case >> } >> >> return 0; >> @@ -340,7 +345,8 @@ >> channel->lo = FIELD_GET(PWM_LOW_MASK, value); >> channel->hi = FIELD_GET(PWM_HIGH_MASK, value); >> >> - state->period = meson_pwm_cnt_to_ns(chip, pwm, channel->lo + channel->hi); >> + state->period = meson_pwm_cnt_to_ns(chip, pwm, >> + channel->lo + 1 + channel->hi + 1); >> state->duty_cycle = meson_pwm_cnt_to_ns(chip, pwm, channel->hi); >> > Doesn't channel->hi have to be incremented here too? Yes, lost the line. I'll fix it Best regards George >> return 0; >