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Message-ID: <20141006104634.GE25202@ulmo>
Date: Mon, 6 Oct 2014 12:46:35 +0200
From: Thierry Reding <thierry.reding@...il.com>
To: Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc: David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
Nicolas Ferre <nicolas.ferre@...el.com>,
Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
Andrew Victor <linux@...im.org.za>,
Samuel Ortiz <sameo@...ux.intel.com>,
Lee Jones <lee.jones@...aro.org>, linux-pwm@...r.kernel.org,
Rob Clark <robdclark@...il.com>,
linux-arm-kernel@...ts.infradead.org,
Rob Herring <robh+dt@...nel.org>,
Pawel Moll <pawel.moll@....com>,
Mark Rutland <mark.rutland@....com>,
Ian Campbell <ijc+devicetree@...lion.org.uk>,
Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, Mark Yao <mark.yao@...k-chips.com>
Subject: Re: [PATCH v7 03/11] pwm: add support for atmel-hlcdc-pwm device
On Wed, Oct 01, 2014 at 04:53:00PM +0200, Boris Brezillon wrote:
[...]
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index b800783..afb896b 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -50,6 +50,16 @@ config PWM_ATMEL
> To compile this driver as a module, choose M here: the module
> will be called pwm-atmel.
>
> +config PWM_ATMEL_HLCDC_PWM
> + tristate "Atmel HLCDC PWM support"
> + select MFD_ATMEL_HLCDC
> + depends on OF
This isn't really necessary since MFD_ATMEL_HLCDC already depends on OF.
> diff --git a/drivers/pwm/pwm-atmel-hlcdc.c b/drivers/pwm/pwm-atmel-hlcdc.c
[...]
> new file mode 100644
> index 0000000..0238f7a
> --- /dev/null
> +++ b/drivers/pwm/pwm-atmel-hlcdc.c
> @@ -0,0 +1,229 @@
> +/*
> + * Copyright (C) 2014 Free Electrons
> + * Copyright (C) 2014 Atmel
> + *
> + * Author: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/mfd/atmel-hlcdc.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/regmap.h>
> +
> +#define ATMEL_HLCDC_PWMCVAL_MASK GENMASK(15, 8)
> +#define ATMEL_HLCDC_PWMCVAL(x) ((x << 8) & ATMEL_HLCDC_PWMCVAL_MASK)
You might want to use an extra pair of parentheses around the "x" above.
> +struct atmel_hlcdc_pwm_chip {
Can we make this...
> + struct pwm_chip chip;
> + struct atmel_hlcdc *hlcdc;
> + struct clk *cur_clk;
> +};
> +
> +static inline struct atmel_hlcdc_pwm_chip *
> +pwm_chip_to_atmel_hlcdc_pwm_chip(struct pwm_chip *chip)
... and this a little shorter? There is a lot of line-wrapping below
only because this is very long. It seems like just dropping the
pwm_chip_ prefix on this function would be enough to not exceed the
78/80 character limit.
> +{
> + return container_of(chip, struct atmel_hlcdc_pwm_chip, chip);
> +}
> +
> +static int atmel_hlcdc_pwm_config(struct pwm_chip *c,
> + struct pwm_device *pwm,
> + int duty_ns, int period_ns)
> +{
> + struct atmel_hlcdc_pwm_chip *chip =
> + pwm_chip_to_atmel_hlcdc_pwm_chip(c);
> + struct atmel_hlcdc *hlcdc = chip->hlcdc;
> + struct clk *new_clk = hlcdc->slow_clk;
> + u64 pwmcval = duty_ns * 256;
> + unsigned long clk_freq;
> + u64 clk_period_ns;
> + u32 pwmcfg;
> + int pres;
> +
> + clk_freq = clk_get_rate(new_clk);
> + clk_period_ns = 1000000000;
NSEC_PER_SEC?
> + clk_period_ns *= 256;
Perhaps collapse the above two in a single line:
clk_period_ns = NSEC_PER_SEC * 256;
?
> + do_div(clk_period_ns, clk_freq);
> +
> + if (clk_period_ns > period_ns) {
> + new_clk = hlcdc->sys_clk;
> + clk_freq = clk_get_rate(new_clk);
> + clk_period_ns = 1000000000;
> + clk_period_ns *= 256;
Maybe:
clk_period_ns = NSEC_PER_SEC * 256;
?
> + do_div(clk_period_ns, clk_freq);
> + }
> +
> + for (pres = 0; pres <= ATMEL_HLCDC_PWMPS_MAX; pres++) {
> + if ((clk_period_ns << pres) >= period_ns)
> + break;
> + }
Technically there's no need for the curly braces.
> +
> + if (pres > ATMEL_HLCDC_PWMPS_MAX)
> + return -EINVAL;
I think the condition above needs to be "pres == ATMEL_HLCDC_PWMPS_MAX",
otherwise this will never be true.
> +
> + pwmcfg = ATMEL_HLCDC_PWMPS(pres);
> +
> + if (new_clk != chip->cur_clk) {
> + u32 gencfg = 0;
> +
> + clk_prepare_enable(new_clk);
This can fail so it needs error-checking.
> + clk_disable_unprepare(chip->cur_clk);
> + chip->cur_clk = new_clk;
> +
> + if (new_clk != hlcdc->slow_clk)
> + gencfg = ATMEL_HLCDC_CLKPWMSEL;
There are lots of negations here, which caused me to think that there
was a third clock involved here, but it seems like new_clk can either be
slow_clk or sys_clk.
Perhaps making this condition "new_clk == hlcdc->sys_clk" would improve
clarity here. Maybe a comment somewhere would help?
> + regmap_update_bits(hlcdc->regmap, ATMEL_HLCDC_CFG(0),
> + ATMEL_HLCDC_CLKPWMSEL, gencfg);
> + }
> +
> + do_div(pwmcval, period_ns);
> + if (pwmcval > 255)
The PWM core already makes sure that duty_ns <= period_ns, so pwmcval
could be anywhere between 0 and 256 here. Where does the disconnect come
from? Why not make pwmcval = duty_ns * 255 if that's the maximum?
> + pwmcval = 255;
> +
> + pwmcfg |= ATMEL_HLCDC_PWMCVAL(pwmcval);
> +
> + regmap_update_bits(hlcdc->regmap, ATMEL_HLCDC_CFG(6),
> + ATMEL_HLCDC_PWMCVAL_MASK | ATMEL_HLCDC_PWMPS_MASK,
> + pwmcfg);
> +
> + return 0;
> +}
> +
> +static int atmel_hlcdc_pwm_set_polarity(struct pwm_chip *c,
> + struct pwm_device *pwm,
> + enum pwm_polarity polarity)
> +{
> + struct atmel_hlcdc_pwm_chip *chip =
> + pwm_chip_to_atmel_hlcdc_pwm_chip(c);
> + struct atmel_hlcdc *hlcdc = chip->hlcdc;
> + u32 cfg = 0;
> +
> + if (polarity == PWM_POLARITY_NORMAL)
> + cfg = ATMEL_HLCDC_PWMPOL;
That's strange. Inverse polarity is the default on this hardware?
> +static int atmel_hlcdc_pwm_enable(struct pwm_chip *c,
> + struct pwm_device *pwm)
There's no need for line-wrapping here. The above fits on one line just
fine.
> +{
> + struct atmel_hlcdc_pwm_chip *chip =
> + pwm_chip_to_atmel_hlcdc_pwm_chip(c);
> + struct atmel_hlcdc *hlcdc = chip->hlcdc;
> + u32 status;
> +
> + regmap_write(hlcdc->regmap, ATMEL_HLCDC_EN, ATMEL_HLCDC_PWM);
> + while (!regmap_read(hlcdc->regmap, ATMEL_HLCDC_SR, &status) &&
> + !(status & ATMEL_HLCDC_PWM))
> + ;
This loop isn't very readable. Can you improve it? Perhaps:
do {
err = regmap_read(hlcdc->regmap, ATMEL_HLCDC_SR, &status);
if (err < 0)
return err;
} while ((status & ATMEL_HLCDC_PWM) == 0);
That also allows errors to be properly propagated. Perhaps you also want
to put a usleep_range() or similar in there.
> +static void atmel_hlcdc_pwm_disable(struct pwm_chip *c,
> + struct pwm_device *pwm)
> +{
> + struct atmel_hlcdc_pwm_chip *chip =
> + pwm_chip_to_atmel_hlcdc_pwm_chip(c);
> + struct atmel_hlcdc *hlcdc = chip->hlcdc;
> + u32 status;
> +
> + regmap_write(hlcdc->regmap, ATMEL_HLCDC_DIS, ATMEL_HLCDC_PWM);
> + while (!regmap_read(hlcdc->regmap, ATMEL_HLCDC_SR, &status) &&
> + (status & ATMEL_HLCDC_PWM))
> + ;
Same here.
> +static int atmel_hlcdc_pwm_probe(struct platform_device *pdev)
> +{
> + struct atmel_hlcdc_pwm_chip *chip;
> + struct device *dev = &pdev->dev;
> + struct atmel_hlcdc *hlcdc;
> + int ret;
> +
> + hlcdc = dev_get_drvdata(dev->parent);
> + if (!hlcdc)
> + return -EINVAL;
Can this really happen?
> + ret = clk_prepare_enable(hlcdc->periph_clk);
> + if (ret)
> + return ret;
> +
> + chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
> + if (!chip)
> + return -ENOMEM;
Don't you want to disable and unprepare the clock here? Perhaps in order
to avoid this call clk_prepare_enable() only after all resources have
been allocated.
> +MODULE_ALIAS("platform:atmel-hlcdc-pwm");
> +MODULE_AUTHOR("Boris Brezillon <boris.brezillon@...e-electrons.com>");
> +MODULE_DESCRIPTION("Atmel HLCDC PWM driver");
> +MODULE_LICENSE("GPL");
According to the file header this needs to be "GPL v2".
Thierry
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