Date: Thu, 13 Aug 2015 11:19:25 +0800
From: Jisheng Zhang <jszhang@marvell.com>
To: Antoine Tenart <antoine.tenart@free-electrons.com>
CC: <sebastian.hesselbarth@gmail.com>, <thierry.reding@gmail.com>,
        <zmxu@marvell.com>, <linux-arm-kernel@lists.infradead.org>,
        <linux-pwm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/5] pwm: add the Berlin pwm controller driver
Message-ID: <20150813111925.217c0b14@xhacker>
In-Reply-To: <1439387497-6863-2-git-send-email-antoine.tenart@free-electrons.com>
References: <1439387497-6863-1-git-send-email-antoine.tenart@free-electrons.com>
	<1439387497-6863-2-git-send-email-antoine.tenart@free-electrons.com>
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Dear Antoine,

On Wed, 12 Aug 2015 15:51:33 +0200
Antoine Tenart <antoine.tenart@free-electrons.com> wrote:

> Add a PWM controller driver for the Marvell Berlin SoCs. This PWM
> controller has 4 channels.
> 
> Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
> ---
>  drivers/pwm/Kconfig      |   9 ++
>  drivers/pwm/Makefile     |   1 +
>  drivers/pwm/pwm-berlin.c | 227 +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 237 insertions(+)
>  create mode 100644 drivers/pwm/pwm-berlin.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index b1541f40fd8d..1773da8145b8 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -92,6 +92,15 @@ config PWM_BCM2835
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-bcm2835.
>  
> +config PWM_BERLIN
> +	tristate "Berlin PWM support"
> +	depends on ARCH_BERLIN
> +	help
> +	  PWM framework driver for Berlin.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-berlin.
> +
>  config PWM_BFIN
>  	tristate "Blackfin PWM support"
>  	depends on BFIN_GPTIMERS
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index ec50eb5b5a8f..670c5fce8bbb 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM)	+= pwm-atmel-hlcdc.o
>  obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o
>  obj-$(CONFIG_PWM_BCM_KONA)	+= pwm-bcm-kona.o
>  obj-$(CONFIG_PWM_BCM2835)	+= pwm-bcm2835.o
> +obj-$(CONFIG_PWM_BERLIN)	+= pwm-berlin.o
>  obj-$(CONFIG_PWM_BFIN)		+= pwm-bfin.o
>  obj-$(CONFIG_PWM_CLPS711X)	+= pwm-clps711x.o
>  obj-$(CONFIG_PWM_EP93XX)	+= pwm-ep93xx.o
> diff --git a/drivers/pwm/pwm-berlin.c b/drivers/pwm/pwm-berlin.c
> new file mode 100644
> index 000000000000..f89e25ea5c6d
> --- /dev/null
> +++ b/drivers/pwm/pwm-berlin.c
> @@ -0,0 +1,227 @@
> +/*
> + * Marvell Berlin PWM driver
> + *
> + * Copyright (C) 2015 Marvell Technology Group Ltd.
> + *
> + * Antoine Tenart <antoine.tenart@free-electrons.com>
> + *
> + * This file is licensed under the terms of the GNU General Public
> + * License version 2. This program is licensed "as is" without any
> + * warranty of any kind, whether express or implied.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/spinlock.h>
> +
> +#define BERLIN_PWM_EN			0x0
> +#define BERLIN_PWM_CONTROL		0x4
> +#define BERLIN_PWM_DUTY			0x8
> +#define BERLIN_PWM_TCNT			0xc
> +
> +#define BERLIN_PWM_ENABLE		BIT(0)
> +#define BERLIN_PWM_DISABLE		0x0
> +#define BERLIN_PWM_INVERT_POLARITY	BIT(3)
> +#define BERLIN_PWM_PRESCALE_MASK	0x7
> +#define BERLIN_PWM_PRESCALE_MAX		4096
> +#define BERLIN_PWM_MAX_TCNT		65535
> +
> +struct berlin_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *base;
> +	spinlock_t lock;
> +};
> +
> +#define to_berlin_pwm_chip(chip)	\
> +	container_of((chip), struct berlin_pwm_chip, chip)
> +
> +#define berlin_pwm_readl(chip, channel, offset)		\
> +	readl((chip)->base + (channel) * 0x10 + offset)
> +#define berlin_pwm_writel(val, chip, channel, offset)	\
> +	writel(val, (chip)->base + (channel) * 0x10 + offset)

It's better to use relaxed version. In some platforms with PL310 such as
BG2Q, the writel/readl will cost much time on spinning the lock if there's
heavy L2 cache maintenance ongoing, this time cost is not necessary.

And IIRC, in patch V2 review, Sebastian doesn't object to relaxed version.

Thanks,
Jisheng

> +
> +/* prescaler table: {1, 4, 8, 16, 64, 256, 1024, 4096} */
> +static const u32 prescaler_diff_table[] = {
> +	1, 4, 2, 2, 4, 4, 4, 4,
> +};
> +
> +static int berlin_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> +			     int duty_ns, int period_ns)
> +{
> +	struct berlin_pwm_chip *berlin_chip = to_berlin_pwm_chip(chip);
> +	int ret, prescale = 0;
> +	u32 val, duty, period;
> +	u64 cycles;
> +
> +	cycles = clk_get_rate(berlin_chip->clk);
> +	cycles *= period_ns;
> +	do_div(cycles, NSEC_PER_SEC);
> +
> +	while (cycles > BERLIN_PWM_MAX_TCNT)
> +		do_div(cycles, prescaler_diff_table[++prescale]);
> +
> +	if (cycles > BERLIN_PWM_MAX_TCNT)
> +		return -EINVAL;
> +
> +	period = cycles;
> +	cycles *= duty_ns;
> +	do_div(cycles, period_ns);
> +	duty = cycles;
> +
> +	ret = clk_prepare_enable(berlin_chip->clk);
> +	if (ret)
> +		return ret;
> +
> +	spin_lock(&berlin_chip->lock);
> +
> +	val = berlin_pwm_readl(berlin_chip, pwm->hwpwm, BERLIN_PWM_CONTROL);
> +	val &= ~BERLIN_PWM_PRESCALE_MASK;
> +	val |= prescale;
> +	berlin_pwm_writel(val, berlin_chip, pwm->hwpwm, BERLIN_PWM_CONTROL);
> +
> +	berlin_pwm_writel(duty, berlin_chip, pwm->hwpwm, BERLIN_PWM_DUTY);
> +	berlin_pwm_writel(period, berlin_chip, pwm->hwpwm, BERLIN_PWM_TCNT);
> +
> +	spin_unlock(&berlin_chip->lock);
> +
> +	clk_disable_unprepare(berlin_chip->clk);
> +
> +	return 0;
> +}
> +
> +static int berlin_pwm_set_polarity(struct pwm_chip *chip,
> +				   struct pwm_device *pwm,
> +				   enum pwm_polarity polarity)
> +{
> +	struct berlin_pwm_chip *berlin_chip = to_berlin_pwm_chip(chip);
> +	int ret;
> +	u32 val;
> +
> +	ret = clk_prepare_enable(berlin_chip->clk);
> +	if (ret)
> +		return ret;
> +
> +	spin_lock(&berlin_chip->lock);
> +
> +	val = berlin_pwm_readl(berlin_chip, pwm->hwpwm, BERLIN_PWM_CONTROL);
> +
> +	if (polarity == PWM_POLARITY_NORMAL)
> +		val &= ~BERLIN_PWM_INVERT_POLARITY;
> +	else
> +		val |= BERLIN_PWM_INVERT_POLARITY;
> +
> +	berlin_pwm_writel(val, berlin_chip, pwm->hwpwm, BERLIN_PWM_CONTROL);
> +
> +	spin_unlock(&berlin_chip->lock);
> +
> +	clk_disable_unprepare(berlin_chip->clk);
> +
> +	return 0;
> +}
> +
> +static int berlin_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct berlin_pwm_chip *berlin_chip = to_berlin_pwm_chip(chip);
> +	int ret;
> +
> +	ret = clk_prepare_enable(berlin_chip->clk);
> +	if (ret)
> +		return ret;
> +
> +	spin_lock(&berlin_chip->lock);
> +	berlin_pwm_writel(BERLIN_PWM_ENABLE, berlin_chip, pwm->hwpwm, BERLIN_PWM_EN);
> +	spin_unlock(&berlin_chip->lock);
> +
> +	return 0;
> +}
> +
> +static void berlin_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct berlin_pwm_chip *berlin_chip = to_berlin_pwm_chip(chip);
> +
> +	spin_lock(&berlin_chip->lock);
> +	berlin_pwm_writel(BERLIN_PWM_DISABLE, berlin_chip, pwm->hwpwm, BERLIN_PWM_EN);
> +	spin_unlock(&berlin_chip->lock);
> +
> +	clk_disable_unprepare(berlin_chip->clk);
> +}
> +
> +static const struct pwm_ops berlin_pwm_ops = {
> +	.config = berlin_pwm_config,
> +	.set_polarity = berlin_pwm_set_polarity,
> +	.enable = berlin_pwm_enable,
> +	.disable = berlin_pwm_disable,
> +	.owner = THIS_MODULE,
> +};
> +
> +static const struct of_device_id berlin_pwm_match[] = {
> +	{ .compatible = "marvell,berlin-pwm" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, berlin_pwm_match);
> +
> +static int berlin_pwm_probe(struct platform_device *pdev)
> +{
> +	struct berlin_pwm_chip *pwm;
> +	struct resource *res;
> +	int ret;
> +
> +	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
> +	if (!pwm)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	pwm->base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(pwm->base))
> +		return PTR_ERR(pwm->base);
> +
> +	pwm->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(pwm->clk))
> +		return PTR_ERR(pwm->clk);
> +
> +	pwm->chip.dev = &pdev->dev;
> +	pwm->chip.ops = &berlin_pwm_ops;
> +	pwm->chip.base = -1;
> +	pwm->chip.npwm = 4;
> +	pwm->chip.can_sleep = true;
> +	pwm->chip.of_xlate = of_pwm_xlate_with_flags;
> +	pwm->chip.of_pwm_n_cells = 3;
> +
> +	spin_lock_init(&pwm->lock);
> +
> +	ret = pwmchip_add(&pwm->chip);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "Failed to add PWM chip: %d\n", ret);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, pwm);
> +
> +	return 0;
> +}
> +
> +static int berlin_pwm_remove(struct platform_device *pdev)
> +{
> +	struct berlin_pwm_chip *pwm = platform_get_drvdata(pdev);
> +
> +	return pwmchip_remove(&pwm->chip);
> +}
> +
> +static struct platform_driver berlin_pwm_driver = {
> +	.probe	= berlin_pwm_probe,
> +	.remove	= berlin_pwm_remove,
> +	.driver	= {
> +		.name	= "berlin-pwm",
> +		.of_match_table = berlin_pwm_match,
> +	},
> +};
> +module_platform_driver(berlin_pwm_driver);
> +
> +MODULE_AUTHOR("Antoine Tenart <antoine.tenart@free-electrons.com>");
> +MODULE_DESCRIPTION("Marvell Berlin PWM driver");
> +MODULE_LICENSE("GPL v2");

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