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From: Baruch Siach <baruch@tkos.co.il>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	linux-pwm@vger.kernel.org,
	Linus Walleij <linus.walleij@linaro.org>,
	Chris Packham <chris.packham@alliedtelesis.co.nz>,
	Russell King <linux@armlinux.org.uk>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	g@pengutronix.de, Thierry Reding <thierry.reding@gmail.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	linux-gpio@vger.kernel.org,
	Ralph Sennhauser <ralph.sennhauser@gmail.com>,
	Lee Jones <lee.jones@linaro.org>,
	Gregory Clement <gregory.clement@bootlin.com>,
	linux-arm-kernel@lists.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Subject: Re: [PATCH 1/5] gpio: mvebu: fix pwm get_state period calculation
Date: Wed, 13 Jan 2021 08:36:12 +0200	[thread overview]
Message-ID: <87ft35xs0z.fsf@tarshish> (raw)
In-Reply-To: <20210111201711.ym46w7dy62ux66zb@pengutronix.de>

Hi Uwe,

On Mon, Jan 11 2021, Uwe Kleine-König wrote:
> $Subject ~= s/get_state/.get_state/ ?

Ack.

> On Mon, Jan 11, 2021 at 01:17:02PM +0200, Baruch Siach wrote:
>> The period is the sum of on and off values.
>> 
>> Reported-by: Russell King <linux@armlinux.org.uk>
>> Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
>> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
>> ---
>>  drivers/gpio/gpio-mvebu.c | 19 ++++++++-----------
>>  1 file changed, 8 insertions(+), 11 deletions(-)
>> 
>> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
>> index 672681a976f5..a912a8fed197 100644
>> --- a/drivers/gpio/gpio-mvebu.c
>> +++ b/drivers/gpio/gpio-mvebu.c
>> @@ -676,20 +676,17 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
>>  	else
>>  		state->duty_cycle = 1;
>>  
>> +	val = (unsigned long long) u; /* on duration */
>>  	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
>> -	val = (unsigned long long) u * NSEC_PER_SEC;
>> +	val += (unsigned long long) u; /* period = on + off duration */
>> +	val *= NSEC_PER_SEC;
>>  	do_div(val, mvpwm->clk_rate);
>> -	if (val < state->duty_cycle) {
>> +	if (val > UINT_MAX)
>> +		state->period = UINT_MAX;
>> +	else if (val)
>> +		state->period = val;
>> +	else
>>  		state->period = 1;
>> -	} else {
>> -		val -= state->duty_cycle;
>> -		if (val > UINT_MAX)
>> -			state->period = UINT_MAX;
>> -		else if (val)
>> -			state->period = val;
>> -		else
>> -			state->period = 1;
>> -	}
>
> The patch looks good, the patch description could be a bit more verbose.
> Something like:
>
> 	Calculate the period as
>
> 		($on + $off) / clkrate
>
> 	instead of
>
> 		$off / clkrate - $on / clkrate
>
> 	.

I take this to refer to the next patch (2/5). This patch changes from
buggy

  $on / clkrate

to

  ($on + $off) / clkrate

baruch

-- 
                                                     ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -

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  reply	other threads:[~2021-01-13  6:37 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-11 11:17 [PATCH 0/5] gpio: mvebu: pwm fixes and improvements Baruch Siach
2021-01-11 11:17 ` [PATCH 1/5] gpio: mvebu: fix pwm get_state period calculation Baruch Siach
2021-01-11 20:17   ` Uwe Kleine-König
2021-01-13  6:36     ` Baruch Siach [this message]
2021-01-13  8:17       ` Uwe Kleine-König
2021-01-11 11:17 ` [PATCH 2/5] gpio: mvebu: improve pwm period calculation accuracy Baruch Siach
2021-01-11 20:18   ` Uwe Kleine-König
2021-01-11 11:17 ` [PATCH 3/5] gpio: mvebu: make pwm apply/get_state closer to idempotent Baruch Siach
2021-01-11 20:20   ` Uwe Kleine-König
2021-01-11 11:17 ` [PATCH 4/5] gpio: mvebu: don't limit pwm period/duty_cycle to UINT_MAX Baruch Siach
2021-01-11 20:21   ` Uwe Kleine-König
2021-01-11 11:17 ` [PATCH 5/5] gpio: mvebu: document zero pwm duty cycle limitation Baruch Siach
2021-01-11 20:24   ` Uwe Kleine-König
2021-01-11 22:43     ` Russell King - ARM Linux admin

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