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Date: Fri, 3 Jul 2020 18:15:56 +0200
From: Jonathan Neuschäfer <j.neuschaefer@....net>
To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: Jonathan Neuschäfer <j.neuschaefer@....net>,
linux-kernel@...r.kernel.org,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
Heiko Stuebner <heiko@...ech.de>, linux-pwm@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>,
Thierry Reding <thierry.reding@...il.com>,
Fabio Estevam <festevam@...il.com>, linux-rtc@...r.kernel.org,
Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
Sam Ravnborg <sam@...nborg.org>,
Andreas Kemnade <andreas@...nade.info>,
NXP Linux Team <linux-imx@....com>,
devicetree@...r.kernel.org, Stephan Gerhold <stephan@...hold.net>,
allen <allen.chen@....com.tw>,
Sascha Hauer <s.hauer@...gutronix.de>,
Lubomir Rintel <lkundrak@...sk>,
Rob Herring <robh+dt@...nel.org>,
Lee Jones <lee.jones@...aro.org>,
linux-arm-kernel@...ts.infradead.org,
Alessandro Zummo <a.zummo@...ertech.it>,
Mark Brown <broonie@...nel.org>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Heiko Stuebner <heiko.stuebner@...obroma-systems.com>,
Josua Mayer <josua.mayer@....eu>,
Shawn Guo <shawnguo@...nel.org>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH 06/10] pwm: ntxec: Add driver for PWM function in
Netronix EC
On Mon, Jun 22, 2020 at 10:18:02AM +0200, Uwe Kleine-König wrote:
> Hello,
>
> On Sun, Jun 21, 2020 at 12:42:17AM +0200, Jonathan Neuschäfer wrote:
> > The Netronix EC provides a PWM output, which is used for the backlight
>
> s/,//
>
> > on ebook readers. This patches adds a driver for the PWM output.
>
> on *some* ebook readers
Ok, I'll fix these.
>
> > +#define NTXEC_UNK_A 0xa1
> > +#define NTXEC_UNK_B 0xa2
> > +#define NTXEC_ENABLE 0xa3
> > +#define NTXEC_PERIOD_LOW 0xa4
> > +#define NTXEC_PERIOD_HIGH 0xa5
> > +#define NTXEC_DUTY_LOW 0xa6
> > +#define NTXEC_DUTY_HIGH 0xa7
> > +
> > +/*
> > + * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
> > + * measured in this unit.
> > + */
> > +static int ntxec_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm_dev,
> > + int duty_ns, int period_ns)
> > +{
> > + struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
> > + uint64_t duty = duty_ns;
> > + uint64_t period = period_ns;
>
> As you cannot use values bigger than 8191999 anyhow, I wonder why you
> use a 64 bit type here.
No particular reason; I possibly got confused by the division API. I'll
use uint32_t instead.
> > + int res = 0;
> > +
> > + do_div(period, 125);
>
> Please use a define instead of plain 125.
Will do.
> > + if (period > 0xffff) {
> > + dev_warn(pwm->dev,
> > + "Period is not representable in 16 bits: %llu\n", period);
> > + return -ERANGE;
> > + }
> > +
> > + do_div(duty, 125);
> > + if (duty > 0xffff) {
> > + dev_warn(pwm->dev, "Duty cycle is not representable in 16 bits: %llu\n",
> > + duty);
> > + return -ERANGE;
> > + }
>
> This check isn't necessary as the pwm core ensures that duty <= period.
Ok, I'll remove it.
>
> > + res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_HIGH, period >> 8);
> > + res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_LOW, period);
> > + res |= ntxec_write8(pwm->ec, NTXEC_DUTY_HIGH, duty >> 8);
> > + res |= ntxec_write8(pwm->ec, NTXEC_DUTY_LOW, duty);
>
> Does this complete the currently running period? Can it happen that a
> new period starts between the first and the last write and so a mixed
> period can be seen at the output?
Good question. I haven't measured it, and also don't have the code
running on the EC.
>
> > +
> > + return (res < 0) ? -EIO : 0;
> > +}
> > +
> > +static int ntxec_pwm_enable(struct pwm_chip *chip,
> > + struct pwm_device *pwm_dev)
> > +{
> > + struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
> > +
> > + return ntxec_write8(pwm->ec, NTXEC_ENABLE, 1);
> > +}
> > +
> > +static void ntxec_pwm_disable(struct pwm_chip *chip,
> > + struct pwm_device *pwm_dev)
> > +{
> > + struct ntxec_pwm *pwm = pwmchip_to_pwm(chip);
> > +
> > + ntxec_write8(pwm->ec, NTXEC_ENABLE, 0);
> > +}
> > +
> > +static struct pwm_ops ntxec_pwm_ops = {
> > + .config = ntxec_pwm_config,
> > + .enable = ntxec_pwm_enable,
> > + .disable = ntxec_pwm_disable,
> > + .owner = THIS_MODULE,
>
> Please don't align the =, just a single space before them is fine.
Ok
> More important: Please implement .apply() (and .get_state()) instead of
> the old API. Also please enable PWM_DEBUG which might save us a review
> iteration.
Will do!
>
> > +};
> > +
> > +static int ntxec_pwm_probe(struct platform_device *pdev)
> > +{
> > + struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);
> > + struct ntxec_pwm *pwm;
> > + struct pwm_chip *chip;
> > + int res;
> > +
> > + pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
> > + if (!pwm)
> > + return -ENOMEM;
> > +
> > + pwm->ec = ec;
> > + pwm->dev = &pdev->dev;
> > +
> > + chip = &pwm->chip;
> > + chip->dev = &pdev->dev;
> > + chip->ops = &ntxec_pwm_ops;
> > + chip->base = -1;
> > + chip->npwm = 1;
> > +
> > + res = pwmchip_add(chip);
> > + if (res < 0)
> > + return res;
> > +
> > + platform_set_drvdata(pdev, pwm);
> > +
> > + res |= ntxec_write8(pwm->ec, NTXEC_ENABLE, 0);
> > + res |= ntxec_write8(pwm->ec, NTXEC_UNK_A, 0xff);
> > + res |= ntxec_write8(pwm->ec, NTXEC_UNK_B, 0xff);
> > +
> > + return (res < 0) ? -EIO : 0;
>
> This is broken for several reasons:
>
> - You're not supposed to modify the output in .probe
> - if ntxec_write8 results in an error you keep the pwm registered.
> - From the moment on pwmchip_add returns the callbacks can be called.
> The calls to ntxec_write8 probably interfere here.
Ok, I'll rework the probe function to avoid these issues.
Thanks for the review,
Jonathan Neuschäfer
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