[RFC] PWM: Add support for pwm-bcm2835

[Johannes Thumshirn <morbidrsa@gmail.com>]

Add support for the PWM controller of the BCM2835 SoC found on Raspberry PI

The driver isn't as much tested as I wanted it to be and devicetree
support is still missing, but I thought it would be nice to have some
comments if I'm in the right direction.

Signed-off-by: Johannes Thumshirn <morbidrsa@gmail.com>
---
 drivers/pwm/Kconfig       |   8 ++
 drivers/pwm/Makefile      |   1 +
 drivers/pwm/pwm-bcm2835.c | 275 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 284 insertions(+)
 create mode 100644 drivers/pwm/pwm-bcm2835.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 75840b5..5417159 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -224,4 +224,12 @@ config PWM_VT8500
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-vt8500.
 
+config PWM_BCM2835
+       tristate "BCM2835 PWM support"
+       help
+        Generic PWM framework driver for bcm2835 found on the Rasperry PI
+
+	To compile this driver as a module, choose M here: the module will be
+	called pwm-bcm2835
+
 endif
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 77a8c18..0cf8d4d 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -20,3 +20,4 @@ obj-$(CONFIG_PWM_TIPWMSS)	+= pwm-tipwmss.o
 obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o
 obj-$(CONFIG_PWM_TWL_LED)	+= pwm-twl-led.o
 obj-$(CONFIG_PWM_VT8500)	+= pwm-vt8500.o
+obj-$(CONFIG_PWM_BCM2835)	+= pwm-bcm2835.o
diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
new file mode 100644
index 0000000..8a64666
--- /dev/null
+++ b/drivers/pwm/pwm-bcm2835.c
@@ -0,0 +1,275 @@
+/*
+ * BCM2835 PWM driver
+ *
+ * Derived from the Tegra PWM driver by NVIDIA Corporation.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * 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.
+ */
+
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/of.h>
+#include <linux/pwm.h>
+
+#define NPWM 2
+
+/* Address Mappings (offsets) from Broadcom BCM2835 ARM Periperals Manual
+ * Section 9.6 Page 141ff
+ */
+#define BCM2835_PWM_CTL		0x00 /* Control register */
+#define BCM2835_PWM_STA		0x04 /* Status register */
+#define BCM2835_PWM_DMAC	0x08 /* PWM DMA Configuration */
+#define BCM2835_PWM_RNG1	0x10 /* PWM Channel 1 Range */
+#define BCM2835_PWM_DAT1	0x14 /* PWM Channel 1 Data */
+#define BCM2835_PWM_FIF1	0x18 /* PWM FIFO Input */
+#define BCM2835_PWM_RNG2	0x20 /* PWM Channel 2 Range */
+#define BCM2835_PWM_DAT2	0x24 /* PWM Channel 2 Data */
+
+/* Control registers 0 and 1 are mirrored on a distance of 4 bits */
+#define HWPWM(x) ((x) << 4)
+
+/* TODO: We only need this register set once and use HWPWM macro to
+ * access 2nd output
+ */
+/* Control Register Bits */
+#define BCM2835_PWM_CTL_PWEN1	BIT(0)	/* Channel 1 enable (RW) */
+#define BCM2835_PWM_CTL_MODE1	BIT(1)	/* Channel 1 mode (RW) */
+#define BCM2835_PWM_CTL_RPTL1	BIT(2)	/* Channel 1 repeat last data (RW) */
+#define BCM2835_PWM_CTL_SBIT1	BIT(3)	/* Channel 1 silence bit (RW) */
+#define BCM2835_PWM_CTL_POLA1	BIT(4)	/* Channel 1 polarity (RW) */
+#define BCM2835_PWM_CTL_USEF1	BIT(5)	/* Channel 1 use FIFO (RW) */
+#define BCM2835_PWM_CTL_CLRF1	BIT(6)	/* Channel 1 clear FIFO (RO) */
+#define BCM2835_PWM_CTL_MSEN1	BIT(7)	/* Channel 1 M/S enable (RW) */
+#define BCM2835_PWM_CTL_PWEN2	BIT(8)	/* Channel 2 enable (RW) */
+#define BCM2835_PWM_CTL_MODE2	BIT(9)	/* Channel 2 mode (RW) */
+#define BCM2835_PWM_CTL_RPTL2	BIT(10)	/* Channel 2 repeat last data (RW) */
+#define BCM2835_PWM_CTL_SBIT2	BIT(11)	/* Channel 2 silence bit (RW) */
+#define BCM2835_PWM_CTL_POLA2	BIT(12)	/* Channel 2 polarity (RW) */
+#define BCM2835_PWM_CTL_USEF2	BIT(13)	/* Channel 2 use FIFO (RW) */
+/* Bit 14 is reserved */
+#define BCM2835_PWM_MSEN2	BIT(15)	/* Channel 2 M/S enable (RW) */
+/* Bits 16 - 31 are reserved */
+
+/* Status Register Bits */
+#define BCM2835_PWM_STA_FULL1	BIT(0)	/* FIFO full flag (RW) */
+#define BCM2835_PWM_STA_EMPT1	BIT(1)	/* FIFO empty flag (RW) */
+#define BCM2835_PWM_STA_WERR1	BIT(2)	/* FIFO write error flag (RW) */
+#define BCM2835_PWM_STA_RERR1	BIT(3)	/* FIFO read error flag (RW) */
+#define BCM2835_PWM_STA_GAPO1	BIT(4)	/* Channel 1 gap occured (RW) */
+#define BCM2835_PWM_STA_GAPO2	BIT(5)	/* Channel 2 gap occured (RW) */
+#define BCM2835_PWM_STA_GAPO3	BIT(6)	/* Channel 3 gap occured (RW) */
+#define BCM2835_PWM_STA_GAPO4	BIT(7)	/* Channel 4 gap occured (RW) */
+#define BCM2835_PWM_STA_BERR	BIT(8)	/* Bus error flag (RW) */
+#define BCM2835_PWM_STA_STA1	BIT(9)	/* Channel 1 state (RW) */
+#define BCM2835_PWM_STA_STA2	BIT(10)	/* Channel 1 state (RW) */
+#define BCM2835_PWM_STA_STA3	BIT(11)	/* Channel 1 state (RW) */
+#define BCM2835_PWM_STA_STA4	BIT(12)	/* Channel 1 state (RW) */
+/* Bits 13 - 31 are reserved */
+
+struct bcm2835_pwm_dev {
+	struct pwm_chip chip;
+	struct device *dev;
+	struct clk *clk;
+	void __iomem *mmio_base;
+};
+
+static inline struct bcm2835_pwm_dev *to_bcm(struct pwm_chip *chip)
+{
+	return container_of(chip, struct bcm2835_pwm_dev, chip);
+}
+
+static inline u32 bcm2835_readl(struct bcm2835_pwm_dev *chip,
+				unsigned int hwpwm, unsigned int num)
+{
+	num <<= HWPWM(hwpwm);
+	return readl(chip->mmio_base + num);
+}
+
+static inline void bcm2835_writel(struct bcm2835_pwm_dev *chip,
+				  unsigned int hwpwm, unsigned int num,
+				  unsigned long val)
+{
+	num <<= HWPWM(hwpwm);
+	writel(val, chip->mmio_base + num);
+}
+
+static int bcm2835_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
+			      int duty_ns, int period_ns)
+{
+	struct bcm2835_pwm_dev *bcm = to_bcm(chip);
+
+	if (WARN_ON(!bcm))
+		return -ENODEV;
+
+	if (duty_ns < 1) {
+		dev_err(bcm->dev, "duty is out of range: %d < 1\n", duty_ns);
+		return -ERANGE;
+	}
+
+	if (period_ns < 1) {
+		dev_err(bcm->dev, "period is out of range: %d < 1\n",
+			period_ns);
+		return -ERANGE;
+	}
+
+	/* disable PWM */
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_CTL, 0);
+
+	/* write period */
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_RNG1, period_ns);
+
+	/* write duty */
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_DAT1, duty_ns);
+
+	/* start PWM */
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_CTL, BCM2835_PWM_CTL_PWEN1);
+
+	return 0;
+}
+
+static int bcm2835_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct bcm2835_pwm_dev *bcm = to_bcm(chip);
+	int rc = 0;
+	u32 val;
+
+	if (WARN_ON(!bcm))
+		return -ENODEV;
+
+	rc = clk_prepare_enable(bcm->clk);
+	if (rc < 0)
+		return rc;
+
+	val = bcm2835_readl(bcm, pwm->hwpwm, BCM2835_PWM_CTL);
+	val |= BCM2835_PWM_CTL_PWEN1;
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_CTL, val);
+
+	return 0;
+}
+
+static void bcm2835_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct bcm2835_pwm_dev *bcm = to_bcm(chip);
+	u32 val;
+
+	if (WARN_ON(!bcm))
+		return;
+
+	val = bcm2835_readl(bcm, pwm->hwpwm, BCM2835_PWM_CTL);
+	val &= ~BCM2835_PWM_CTL_PWEN1;
+	bcm2835_writel(bcm, pwm->hwpwm, BCM2835_PWM_CTL, val);
+
+	clk_disable_unprepare(bcm->clk);
+}
+
+static int bcm2835_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
+				enum pwm_polarity polarity)
+{
+	struct bcm2835_pwm_dev *bcm = to_bcm(chip);
+	u32 val;
+
+	if (WARN_ON(!bcm))
+		return -ENODEV;
+
+	val = bcm2835_readl(bcm, pwm->hwpwm, BCM2835_PWM_CTL);
+
+	if (polarity == PWM_POLARITY_NORMAL)
+		val |= BCM2835_PWM_CTL_POLA1;
+	else
+		val &= ~BCM2835_PWM_CTL_POLA1;
+
+	return 0;
+}
+
+static const struct pwm_ops bcm2835_pwm_ops = {
+	.config  = bcm2835_pwm_config,
+	.enable  = bcm2835_pwm_enable,
+	.disable = bcm2835_pwm_disable,
+	.set_polarity = bcm2835_set_polarity,
+};
+
+static int bcm2835_pwm_probe(struct platform_device *pdev)
+{
+	struct bcm2835_pwm_dev *bcm;
+	struct resource *r;
+	int ret;
+
+	bcm = devm_kzalloc(&pdev->dev, sizeof(*bcm), GFP_KERNEL);
+	if (!bcm)
+		return -ENOMEM;
+
+	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!r) {
+		dev_err(&pdev->dev, "no memory resource defined\n");
+		return -ENODEV;
+	}
+
+	bcm->mmio_base = devm_ioremap_resource(&pdev->dev, r);
+	if (IS_ERR(bcm->mmio_base))
+		return PTR_ERR(bcm->mmio_base);
+
+	bcm->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(bcm->clk))
+		return PTR_ERR(bcm->clk);
+
+	clk_prepare_enable(bcm->clk);
+
+	bcm->chip.ops = &bcm2835_pwm_ops;
+	bcm->chip.dev = &pdev->dev;
+	bcm->chip.base = -1;
+	bcm->chip.npwm = NPWM;
+
+	ret = pwmchip_add(&bcm->chip);
+	if (ret < 0)
+		return ret;
+
+	platform_set_drvdata(pdev, bcm);
+
+	return 0;
+}
+
+static int bcm2835_pwm_remove(struct platform_device *pdev)
+{
+	struct bcm2835_pwm_dev *bcm = platform_get_drvdata(pdev);
+
+	if (WARN_ON(!bcm))
+		return -ENODEV;
+
+	clk_disable_unprepare(bcm->clk);
+
+	return pwmchip_remove(&bcm->chip);
+}
+
+static const struct of_device_id bcm2835_pwm_of_match[] = {
+	{ .compatible = "brcm,bcm2835-pwm" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, bcm2835_pwm_of_match);
+
+static struct platform_driver bcm2835_pwm_driver = {
+	.probe		= bcm2835_pwm_probe,
+	.remove		= bcm2835_pwm_remove,
+	.driver	= {
+		.name	= "pwm-bcm2835",
+		.owner	= THIS_MODULE,
+		.of_match_table = bcm2835_pwm_of_match,
+	},
+};
+
+module_platform_driver(bcm2835_pwm_driver);
+
+MODULE_AUTHOR("Johannes Thumshirn <morbidrsa@gmail.com>");
+MODULE_DESCRIPTION("BCM2835 PWM driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:pwm-bcm2835");
-- 
1.8.4