Date:	Mon, 23 Sep 2013 17:38:55 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Bo Shen <voice.shen@...el.com>,
	Thierry Reding <thierry.reding@...il.com>
CC:	<plagnioj@...osoft.com>, <linux-pwm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v3] PWM: at91: add Atmel PWM controller driver

On 22/09/2013 10:05, Bo Shen :
> Add Atmel PWM controller driver based on PWM framework.
>
> This is the basic function implementation of Atmel PWM controller.
> It can work with PWM based led and backlight.
>
> Signed-off-by: Bo Shen <voice.shen@...el.com>
> ---
> Changes in v3:
>    - change compatible string from "atmel,sama5-pwm" to "atmel,sama5d3-pwm"
>    - Add PWM led example in binding documentation
>    - Using micro replace hard code
>
> Changes in v2:
>    - Address the comments from Thierry Reding
>
>   .../devicetree/bindings/pwm/atmel-pwm.txt          |   41 +++
>   drivers/pwm/Kconfig                                |    9 +
>   drivers/pwm/Makefile                               |    1 +
>   drivers/pwm/pwm-atmel.c                            |  335 ++++++++++++++++++++
>   4 files changed, 386 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/pwm/atmel-pwm.txt
>   create mode 100644 drivers/pwm/pwm-atmel.c
>
> diff --git a/Documentation/devicetree/bindings/pwm/atmel-pwm.txt b/Documentation/devicetree/bindings/pwm/atmel-pwm.txt
> new file mode 100644
> index 0000000..1c1a5fa
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/atmel-pwm.txt
> @@ -0,0 +1,41 @@
> +Atmel PWM controller
> +
> +Required properties:
> +  - compatible: should be one of:
> +    - "atmel,at91sam9rl-pwm"
> +    - "atmel,sama5d3-pwm"
> +  - reg: physical base address and length of the controller's registers
> +  - #pwm-cells: Should be 3. See pwm.txt in this directory for a
> +    description of the cells format
> +
> +Example:
> +
> +	pwm0: pwm@...34000 {
> +		compatible = "atmel,at91sam9rl-pwm";
> +		reg = <0xf8034000 0x400>;
> +		#pwm-cells = <3>;
> +	};
> +
> +The following the pwm led based example:
> +
> +	pwm0: pwm@...34000 {
> +		compatible = "atmel,at91sam9rl-pwm";
> +		reg = <0xf8034000 0x400>;
> +		#pwm-cells = <3>;
> +	};
> +
> +	pwdleds {
> +		compatible = "pwm-leds";
> +
> +		d1 {
> +			label = "d1";
> +			pwms = <&pwm0 3 5000 0>
> +			max-brightness = <255>;
> +		};
> +
> +		d2 {
> +			label = "d2";
> +			pwms = <&pwm0 1 5000 1>
> +			max-brightness = <255>;
> +		};
> +	};
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 75840b5..54237b9 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -41,6 +41,15 @@ config PWM_AB8500
>   	  To compile this driver as a module, choose M here: the module
>   	  will be called pwm-ab8500.
>
> +config PWM_ATMEL
> +	tristate "Atmel PWM support"
> +	depends on ARCH_AT91
> +	help
> +	  Generic PWM framework driver for Atmel SoC.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-atmel.
> +
>   config PWM_ATMEL_TCB
>   	tristate "Atmel TC Block PWM support"
>   	depends on ATMEL_TCLIB && OF
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 77a8c18..5b193f8 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -1,6 +1,7 @@
>   obj-$(CONFIG_PWM)		+= core.o
>   obj-$(CONFIG_PWM_SYSFS)		+= sysfs.o
>   obj-$(CONFIG_PWM_AB8500)	+= pwm-ab8500.o
> +obj-$(CONFIG_PWM_ATMEL)		+= pwm-atmel.o
>   obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o
>   obj-$(CONFIG_PWM_BFIN)		+= pwm-bfin.o
>   obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> new file mode 100644
> index 0000000..9c86dfe
> --- /dev/null
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -0,0 +1,335 @@
> +/*
> + * Driver for Atmel Pulse Width Modulation Controller
> + *
> + * Copyright (C) 2013 Atmel Corporation
> + *		 Bo Shen <voice.shen@...el.com>
> + *
> + * Licensed under GPLv2.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/slab.h>
> +
> +/* The following is global registers for PWM controller */
> +#define PWM_ENA			0x04
> +#define PWM_DIS			0x08
> +#define PWM_SR			0x0C
> +/* bit field in SR */
> +#define PWM_SR_ALL_CH_ON	0x0F
> +
> +/* The following register is PWM channel related registers */
> +#define PWM_CH_REG_OFFSET	0x200
> +
> +#define PWM_CMR			0x0
> +/* bit field in CMR */
> +#define PWM_CMR_CPOL		(1 << 9)
> +#define PWM_CMR_UPD_CDTY	(1 << 10)
> +
> +/* The following registers for PWM v1 */
> +#define PWMv1_CDTY		0x04
> +#define PWMv1_CPRD		0x08
> +#define PWMv1_CUPD		0x10
> +
> +/* The following registers for PWM v2 */
> +#define PWMv2_CDTY		0x04
> +#define PWMv2_CDTYUPD		0x08
> +#define PWMv2_CPRD		0x0C
> +#define PWMv2_CPRDUPD		0x10
> +
> +/* max value for duty and period */
> +/*
> + * Although the duty and period register is 32 bit,
> + * however only the LSB 16 bits are significant.
> + */
> +#define PWM_MAX_DTY		0xFFFF
> +#define PWM_MAX_PRD		0xFFFF
> +#define PRD_MAX_PRES		10
> +
> +struct atmel_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *base;
> +
> +	void (*config)(struct pwm_chip *chip, struct pwm_device *pwm,
> +		       int dty, int prd);
> +};
> +
> +static inline struct atmel_pwm_chip *to_atmel_pwm_chip(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct atmel_pwm_chip, chip);
> +}
> +
> +static inline u32 atmel_pwm_readl(struct atmel_pwm_chip *chip,
> +				  unsigned long offset)
> +{
> +	return readl(chip->base + offset);
> +}
> +
> +static inline void atmel_pwm_writel(struct atmel_pwm_chip *chip,
> +				    unsigned long offset, unsigned long val)
> +{
> +	writel(val, chip->base + offset);
> +}
> +
> +static inline u32 atmel_pwm_ch_readl(struct atmel_pwm_chip *chip,
> +				     unsigned int ch, unsigned long offset)
> +{
> +	return readl(chip->base + PWM_CH_REG_OFFSET + ch * 0x20 + offset);

Well, even for this 0x20 constant, if it makes senses, it could be good 
to define it as well...


> +}
> +
> +static inline void atmel_pwm_ch_writel(struct atmel_pwm_chip *chip,
> +				       unsigned int ch, unsigned long offset,
> +				       unsigned long val)
> +{
> +	writel(val, chip->base + PWM_CH_REG_OFFSET + ch * 0x20 + offset);

Ditto.

> +}
> +
> +static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> +		int duty_ns, int period_ns)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +	unsigned long clk_rate, prd, dty;
> +	unsigned long long val, div;
> +	int ret, pres = 0;
> +
> +	clk_rate = clk_get_rate(atmel_pwm->clk);
> +	div = clk_rate;
> +
> +	/* Calculate the period cycles */
> +	while (div > PWM_MAX_PRD) {
> +		div = clk_rate / (1 << pres);
> +		div = div * period_ns;
> +		/* 1/Hz = 100000000 ns */
> +		do_div(div, 1000000000);
> +
> +		if (pres++ > PRD_MAX_PRES) {
> +			pr_err("PRES is bigger than maximum pre-scaler\n");
> +			return -EINVAL;
> +		}
> +	}
> +
> +	/* Calculate the duty cycles */
> +	prd = div;
> +	div *= duty_ns;
> +	do_div(div, period_ns);
> +	dty = div;
> +
> +	ret = clk_enable(atmel_pwm->clk);
> +	if (ret) {
> +		pr_err("Failed to enable pwm clock\n");
> +		return ret;
> +	}
> +
> +	atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, pres);
> +	atmel_pwm->config(chip, pwm, dty, prd);
> +
> +	/* Check whether need to disable clock */
> +	val = atmel_pwm_readl(atmel_pwm, PWM_SR);
> +	if ((val & PWM_SR_ALL_CH_ON) == 0)
> +		clk_disable(atmel_pwm->clk);
> +
> +	return 0;
> +}
> +
> +static void atmel_pwm_config_v1(struct pwm_chip *chip, struct pwm_device *pwm,
> +				int dty, int prd)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +	unsigned int val;
> +
> +	/*
> +	 * If the PWM channel is disabled, write value to duty and period
> +	 * registers directly.
> +	 * If the PWM channel is enabled, using the update register, it needs
> +	 * to set bit 10 of CMR to 0
> +	 */
> +	if (test_bit(PWMF_ENABLED, &pwm->flags)) {
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv1_CUPD, dty);
> +
> +		val = atmel_pwm_ch_readl(atmel_pwm, pwm->hwpwm, PWM_CMR);
> +		val &= ~PWM_CMR_UPD_CDTY;
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
> +	} else {
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv1_CDTY, dty);
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv1_CPRD, prd);
> +	}
> +}
> +
> +static void atmel_pwm_config_v2(struct pwm_chip *chip, struct pwm_device *pwm,
> +				int dty, int prd)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +
> +	/*
> +	 * If the PWM channel is disabled, write value to duty and period
> +	 * registers directly.
> +	 * If the PWM channel is enabled, using the duty update register to
> +	 * update the value.
> +	 */
> +	if (test_bit(PWMF_ENABLED, &pwm->flags)) {
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv2_CDTYUPD, dty);
> +	} else {
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv2_CDTY, dty);
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMv2_CPRD, prd);
> +	}
> +}
> +
> +static int atmel_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> +		enum pwm_polarity polarity)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +	u32 val = 0;
> +	int ret;
> +
> +	ret = clk_enable(atmel_pwm->clk);
> +	if (ret) {
> +		pr_err("failed to enable pwm clock\n");
> +		return ret;
> +	}
> +
> +	if (polarity == PWM_POLARITY_NORMAL)
> +		val &= ~PWM_CMR_CPOL;
> +	else
> +		val |= PWM_CMR_CPOL;
> +
> +	atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
> +
> +	clk_disable(atmel_pwm->clk);
> +
> +	return 0;
> +}
> +
> +static int atmel_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +
> +	clk_prepare_enable(atmel_pwm->clk);

I am not sure that "prepare" is needed here as it is done in probe 
function. Please check.

Anyway, whichever the function is, the return code shall be tested.

> +
> +	atmel_pwm_writel(atmel_pwm, PWM_ENA, 1 << pwm->hwpwm);
> +
> +	return 0;
> +}
> +
> +static void atmel_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +	u32 val;
> +
> +	atmel_pwm_writel(atmel_pwm, PWM_DIS, 1 << pwm->hwpwm);
> +
> +	val = atmel_pwm_readl(atmel_pwm, PWM_SR);
> +	if ((val & PWM_SR_ALL_CH_ON) == 0)
> +		clk_disable(atmel_pwm->clk);
> +}
> +
> +static const struct pwm_ops atmel_pwm_ops = {
> +	.config = atmel_pwm_config,
> +	.set_polarity = atmel_pwm_set_polarity,
> +	.enable = atmel_pwm_enable,
> +	.disable = atmel_pwm_disable,
> +	.owner = THIS_MODULE,
> +};
> +
> +struct atmel_pwm_data {
> +	void (*config)(struct pwm_chip *chip, struct pwm_device *pwm,
> +		       int dty, int prd);
> +};
> +
> +static const struct atmel_pwm_data atmel_pwm_data_v1 = {
> +	.config = atmel_pwm_config_v1,
> +};
> +
> +static const struct atmel_pwm_data atmel_pwm_data_v2 = {
> +	.config = atmel_pwm_config_v2,
> +};
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id atmel_pwm_dt_ids[] = {
> +	{
> +		.compatible = "atmel,at91sam9rl-pwm",
> +		.data = &atmel_pwm_data_v1,
> +	}, {
> +		.compatible = "atmel,sama5d3-pwm",
> +		.data = &atmel_pwm_data_v2,
> +	}, {
> +		/* sentinel */
> +	},
> +};
> +MODULE_DEVICE_TABLE(of, atmel_pwm_dt_ids);
> +#endif
> +
> +static int atmel_pwm_probe(struct platform_device *pdev)
> +{
> +	const struct of_device_id *of_id =
> +		of_match_device(atmel_pwm_dt_ids, &pdev->dev);
> +	const struct atmel_pwm_data *data;
> +	struct atmel_pwm_chip *atmel_pwm;
> +	struct resource *res;
> +	int ret;
> +
> +	atmel_pwm = devm_kzalloc(&pdev->dev, sizeof(*atmel_pwm), GFP_KERNEL);
> +	if (!atmel_pwm)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res)
> +		return -ENODEV;
> +
> +	atmel_pwm->base = devm_ioremap_resource(&pdev->dev, res);
> +
> +	atmel_pwm->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(atmel_pwm->clk))
> +		return PTR_ERR(atmel_pwm->clk);
> +	clk_prepare(atmel_pwm->clk);

I think that clk_prepare() can fail and return an error code: please 
check this (even if on at91 it can't fail for the moment).

> +
> +	atmel_pwm->chip.dev = &pdev->dev;
> +	atmel_pwm->chip.ops = &atmel_pwm_ops;
> +	atmel_pwm->chip.of_xlate = of_pwm_xlate_with_flags;
> +	atmel_pwm->chip.of_pwm_n_cells = 3;
> +	atmel_pwm->chip.base = -1;
> +	atmel_pwm->chip.npwm = 4;
> +
> +	data = of_id->data;
> +	atmel_pwm->config = data->config;
> +
> +	ret = pwmchip_add(&atmel_pwm->chip);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "failed to add pwm chip %d\n", ret);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, atmel_pwm);
> +
> +	return 0;
> +}
> +
> +static int atmel_pwm_remove(struct platform_device *pdev)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = platform_get_drvdata(pdev);
> +
> +	clk_unprepare(atmel_pwm->clk);
> +
> +	return pwmchip_remove(&atmel_pwm->chip);
> +}
> +
> +static struct platform_driver atmel_pwm_driver = {
> +	.driver = {
> +		.name = "atmel-pwm",
> +		.of_match_table = of_match_ptr(atmel_pwm_dt_ids),
> +	},
> +	.probe = atmel_pwm_probe,
> +	.remove = atmel_pwm_remove,
> +};
> +module_platform_driver(atmel_pwm_driver);
> +
> +MODULE_ALIAS("platform:atmel-pwm");
> +MODULE_AUTHOR("Bo Shen <voice.shen@...el.com>");
> +MODULE_DESCRIPTION("Atmel PWM driver");
> +MODULE_LICENSE("GPL v2");
>


-- 
Nicolas Ferre
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