From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755617Ab3LDDBu (ORCPT ); Tue, 3 Dec 2013 22:01:50 -0500 Received: from nasmtp01.atmel.com ([192.199.1.245]:64748 "EHLO DVREDG01.corp.atmel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755558Ab3LDDBr (ORCPT ); Tue, 3 Dec 2013 22:01:47 -0500 Message-ID: <529E9AA2.8020400@atmel.com> Date: Wed, 4 Dec 2013 10:59:46 +0800 From: Bo Shen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Thierry Reding CC: , , , , , , , Subject: Re: [PATCH v8 1/2] PWM: atmel-pwm: add PWM controller driver References: <1384766002-2852-1-git-send-email-voice.shen@atmel.com> <20131202105957.GD18060@ulmo.nvidia.com> <529D4B58.9020700@atmel.com> <20131203094326.GB21178@ulmo.nvidia.com> In-Reply-To: <20131203094326.GB21178@ulmo.nvidia.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.168.5.13] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thierry, On 12/03/2013 05:43 PM, Thierry Reding wrote: > On Tue, Dec 03, 2013 at 11:09:12AM +0800, Bo Shen wrote: >> On 12/02/2013 06:59 PM, Thierry Reding wrote: >>> On Mon, Nov 18, 2013 at 05:13:21PM +0800, Bo Shen wrote: > [...] >>>> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c > [...] >>>> + /* Calculate the period cycles */ >>>> + while (div > PWM_MAX_PRD) { >>>> + div = clk_rate / (1 << pres); >>>> + div = div * period_ns; >>>> + /* 1/Hz = 100000000 ns */ >>> >>> I don't think that comment is needed. >> >> This is asked to be added. >> And, I think keep it and it won't hurt, what do you think? > > I think it's obvious that you're converting from nanoseconds because of > the _ns prefix in period_ns. But if somebody requested this and everyone > else thinks it's useful, I'm okay with keeping it. > >>>> + if (test_bit(PWMF_ENABLED, &pwm->flags)) { >>>> + atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTYUPD, dty); >>>> + } else { >>>> + atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTY, dty); >>>> + atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CPRD, prd); >>>> + } >>>> +} >>> >>> Neither version 1 nor version 2 seem to be able to change the period >>> while the channel is enabled. Perhaps that should be checked for in >>> atmel_pwm_config() and an error (-EBUSY) returned? >> >> The period is configured in dt in device tree, or platform data in non >> device tree. Nowhere will update period. So, not code to update period. >> Am I right? If not, please figure out. > > The .config() operation allows the period to be specified. Just because > nobody currently changes it at runtime doesn't mean it can't be done. > > It is also possible that whoever wrote the device tree or platform data > didn't know that the period must be the same for all PWM channels and > therefore might use different values. If you check for this, at least > they'll notice. If you don't check for it, then they may end up having > the period reconfigured behind their backs, which may cause parts of > their setup to behave unexpectedly. Thanks for this information. I will add code for changing period. > Thierry > Best Regards, Bo Shen