Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754459AbcK1IPZ convert rfc822-to-8bit (ORCPT ); Mon, 28 Nov 2016 03:15:25 -0500 Received: from mail.free-electrons.com ([62.4.15.54]:46618 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754245AbcK1IPN (ORCPT ); Mon, 28 Nov 2016 03:15:13 -0500 Date: Mon, 28 Nov 2016 09:15:08 +0100 From: Boris Brezillon To: Lukasz Majewski Cc: Stefan Agner , Thierry Reding , Sascha Hauer , linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org, Fabio Estevam , Fabio Estevam , Lothar Wassmann , Bhuvanchandra DV , kernel@pengutronix.de Subject: Re: [PATCH v3 07/11] pwm: imx: Provide atomic PWM support for i.MX PWMv2 Message-ID: <20161128091508.685324a5@bbrezillon> In-Reply-To: <20161128065031.712d9e7f@jawa> References: <1477984230-18071-1-git-send-email-l.majewski@majess.pl> <1477984230-18071-8-git-send-email-l.majewski@majess.pl> <4f514a235a404d0ab9d26f389fc83f51@agner.ch> <20161123093848.206ad78f@bbrezillon> <20161128065031.712d9e7f@jawa> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8874 Lines: 264 On Mon, 28 Nov 2016 06:50:31 +0100 Lukasz Majewski wrote: > Dear Stefan, Boris, > > > On 2016-11-23 00:38, Boris Brezillon wrote: > > > On Tue, 22 Nov 2016 13:55:33 -0800 > > > Stefan Agner wrote: > > > > > >> On 2016-11-01 00:10, Lukasz Majewski wrote: > > >> > This commit provides apply() callback implementation for i.MX's > > >> > PWMv2. > > >> > > > >> > Suggested-by: Stefan Agner > > >> > Suggested-by: Boris Brezillon > > >> > Signed-off-by: Lukasz > > >> > Majewski Reviewed-by: Boris Brezillon > > >> > --- > > >> > Changes for v3: > > >> > - Remove ipg clock enable/disable functions > > >> > > > >> > Changes for v2: > > >> > - None > > >> > --- > > >> > drivers/pwm/pwm-imx.c | 70 > > >> > +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file > > >> > changed, 70 insertions(+) > > >> > > > >> > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c > > >> > index ebe9b0c..cd53c05 100644 > > >> > --- a/drivers/pwm/pwm-imx.c > > >> > +++ b/drivers/pwm/pwm-imx.c > > >> > @@ -159,6 +159,75 @@ static void imx_pwm_wait_fifo_slot(struct > > >> > pwm_chip *chip, } > > >> > } > > >> > > > >> > +static int imx_pwm_apply_v2(struct pwm_chip *chip, struct > > >> > pwm_device *pwm, > > >> > + struct pwm_state *state) > > >> > +{ > > >> > + unsigned long period_cycles, duty_cycles, prescale; > > >> > + struct imx_chip *imx = to_imx_chip(chip); > > >> > + struct pwm_state cstate; > > >> > + unsigned long long c; > > >> > + u32 cr = 0; > > >> > + int ret; > > >> > + > > >> > + pwm_get_state(pwm, &cstate); > > >> > + > > >> > > >> Couldn't we do: > > >> > > >> if (cstate.enabled) { ... > > >> > > >> > + c = clk_get_rate(imx->clk_per); > > >> > + c *= state->period; > > >> > + > > >> > + do_div(c, 1000000000); > > >> > + period_cycles = c; > > >> > + > > >> > + prescale = period_cycles / 0x10000 + 1; > > >> > + > > >> > + period_cycles /= prescale; > > >> > + c = (unsigned long long)period_cycles * > > >> > state->duty_cycle; > > >> > + do_div(c, state->period); > > >> > + duty_cycles = c; > > >> > + > > >> > + /* > > >> > + * according to imx pwm RM, the real period value > > >> > should be > > >> > + * PERIOD value in PWMPR plus 2. > > >> > + */ > > >> > + if (period_cycles > 2) > > >> > + period_cycles -= 2; > > >> > + else > > >> > + period_cycles = 0; > > >> > + > > >> > + /* Enable the clock if the PWM is being enabled. */ > > >> > + if (state->enabled && !cstate.enabled) { > > >> > + ret = clk_prepare_enable(imx->clk_per); > > >> > + if (ret) > > >> > + return ret; > > >> > + } > > >> > + > > >> > + /* > > >> > + * Wait for a free FIFO slot if the PWM is already > > >> > enabled, and flush > > >> > + * the FIFO if the PWM was disabled and is about to be > > >> > enabled. > > >> > + */ > > >> > + if (cstate.enabled) > > >> > + imx_pwm_wait_fifo_slot(chip, pwm); > > >> > + else if (state->enabled) > > >> > + imx_pwm_sw_reset(chip); > > >> > + > > >> > + writel(duty_cycles, imx->mmio_base + MX3_PWMSAR); > > >> > + writel(period_cycles, imx->mmio_base + MX3_PWMPR); > > >> > + > > >> > + cr |= MX3_PWMCR_PRESCALER(prescale) | > > >> > + MX3_PWMCR_DOZEEN | MX3_PWMCR_WAITEN | > > >> > + MX3_PWMCR_DBGEN | MX3_PWMCR_CLKSRC_IPG_HIGH; > > >> > + > > >> > + if (state->enabled) > > >> > + cr |= MX3_PWMCR_EN; > > >> > > >> } else if (state->enabled) { > > >> imx_pwm_sw_reset(chip); > > >> } > > >> > > >> and get rid of the if (state->enabled) in between? This would safe > > >> us useless recalculation when disabling the controller... > > > > > > I get your point, but I'm pretty sure your proposal does not do what > > > you want (remember that cstate is the current state, and state is > > > the new state to apply). > > > > > > Something like that would work better: > > > > > > if (state->enabled) { > > > > Oops, yes, got that wrong. state->enabled is what I meant. > > > > > c = clk_get_rate(imx->clk_per); > > > c *= state->period; > > > > > > do_div(c, 1000000000); > > > period_cycles = c; > > > > > > prescale = period_cycles / 0x10000 + 1; > > > > > > period_cycles /= prescale; > > > c = (unsigned long long)period_cycles * > > > state->duty_cycle; > > > do_div(c, state->period); > > > duty_cycles = c; > > > > > > /* > > > * According to imx pwm RM, the real period value > > > * should be PERIOD value in PWMPR plus 2. > > > */ > > > if (period_cycles > 2) > > > period_cycles -= 2; > > > else > > > period_cycles = 0; > > > > > > /* > > > * Enable the clock if the PWM is not already > > > * enabled. > > > */ > > > if (!cstate.enabled) { > > > ret = clk_prepare_enable(imx->clk_per); > > > if (ret) > > > return ret; > > > } > > > > > > /* > > > * Wait for a free FIFO slot if the PWM is already > > > * enabled, and flush the FIFO if the PWM was > > > disabled > > > * and is about to be enabled. > > > */ > > > if (cstate.enabled) > > > imx_pwm_wait_fifo_slot(chip, pwm); > > > else > > > imx_pwm_sw_reset(chip); > > > > > > writel(duty_cycles, imx->mmio_base + MX3_PWMSAR); > > > writel(period_cycles, imx->mmio_base + MX3_PWMPR); > > > > > > writel(MX3_PWMCR_PRESCALER(prescale) | > > > MX3_PWMCR_DOZEEN | MX3_PWMCR_WAITEN | > > > MX3_PWMCR_DBGEN | MX3_PWMCR_CLKSRC_IPG_HIGH | > > > MX3_PWMCR_EN, > > > imx->mmio_base + MX3_PWMCR); > > > } else { > > > > > > writel(0, imx->mmio_base + MX3_PWMCR); > > > > > > /* Disable the clock if the PWM is currently > > > enabled. */ if (cstate.enabled) > > > clk_disable_unprepare(imx->clk_per); > > > } > > > > > > > > > This being said, I'm a bit concerned by the way this driver handles > > > PWM config requests. > > > It seems that the new config request is queued, and nothing > > > guarantees > > > > Not sure if that is true. The RM says: "A change in the period value > > due to a write in PWM_PWMPR results in the counter being reset to > > zero and the start of a new count period." > > > > And for PWMSAR: "When a new value is written, the duty cycle changes > > after the current period is over." > > > > So I guess writing the period basically makes sure the next value from > > PWMSAR will be active immediately... > > > > > > > that it is actually applied when the > > > pwm_apply/config/enable/disable() functions return. > > > > > > Given that the driver did it like that since quite some time, I am > > assuming it mostly works in practice. > > > > I would rather prefer to do that conversion to atomic PWM API now, and > > fix that in a second step... > > I'm also for fixing one problem in a time. The "PWM ->apply()" set of > patches now tries to fix all problems in IMX PWM driver. > > Could we agree on the scope of this work? I mean what should be > included to "->apply()" rework and what will be fixed latter? I never asked to fix that in this series ;-), I was just pointing the weird behavior of the existing code. Let's focus on the atomic support for now. > > Frankly, I think that this patch series comes to the point where it is > not manageable anymore. > > Please also keep in mind that I do have iMX6q system, Stefan has imx7 > and Sasha has HW with PWMv1 working. > > Changing the driver in N different places not related to the > "->apply()" atomicity support (the ipg clock, FIFO) requires far more > work and testing. > > > Best regards, > Łukasz Majewski > > > > > > > > > This approach has several flaws IMO: > > > > > > 1/ I'm not sure this is what the PWM users expect. Getting your > > > request queued with no guarantees that it is applied can be weird > > > in some cases (especially when the user changes the PWM config > > > several times in a short period of time). > > > 2/ In the disable path, you queue a "stop PWM" request, but you're > > > not sure that it's actually dequeued before the per clk is disabled. > > > What happens in that case? And more importantly, what happens > > > when the PWM is re-enabled to apply a new config? AFAICS, there > > > might be a short period of time where the re-enabled PWM is > > > actually running with the old config until we flush the command > > > queue and queue a new command. > > > 3/ The queueing approach complicates the whole logic. You have to > > > flush the FIFO in some cases, or wait for an empty slots if too > > > many commands are queued. > > > Forcing imx_pwm_apply_v2() to wait for the config request to be > > > applied should simplify the whole thing, because you will always > > > be guaranteed that the FIFO is empty, and that the current > > > configuration is the last requested one. > > > > > > > -- > > Stefan >