[PATCH V4] PWM: Add SPEAr PWM chip driver support

Shiraz Hashim
2012-10-22T11:07:00Z

Add support for PWM chips present on SPEAr platforms. These PWM
chips support 4 channel output with programmable duty cycle and
frequency.

More details on these PWM chips can be obtained from relevant
chapter of reference manual, present at following[1] location.

1. http://www.st.com/internet/mcu/product/251211.jsp

Cc: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Vipin Kumar <vipin.kumar@st.com>
---
Changes:-
V3 --> V4:
* simplify remove
* maintain alphabetical order in Makefile
* donot check for device node in probe
* move few assignment lines in probe

V2 --> V3:
* remove "disabled" line from pwm dt binding documentation
* remove un-necessary check on pwm chip (for NULL) in remove.

V1 --> V2:
* make proper reference to pwm and pwm chip
* take care to capitalize PWM at appropriate places
* fix compatible string to the SoC where pwm chip was introduced
* Rename the documentation file to the name of driver
* Fix cosmetic changes like names, function name alignment, paragraph
formating, comments placement and formating, etc.
* Group and associate the bit field definitions to their registers
* Fix kerneldoc for structure definition
* Use chip to name pwm device and pwm for the channel instance
* Remove init section qualifiers
* Remove ifdefs around device tree from code and add dependency on CONFIG_OF
* prepare/unprepare clock once in probe/remove and just enable/disable
at rest of the places.
* Use _relaxed for readl/writel.
* Fix pwm disable part in remove

.../devicetree/bindings/pwm/spear-pwm.txt | 18 ++
drivers/pwm/Kconfig | 11 +
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-spear.c | 273 ++++++++++++++++++++
4 files changed, 303 insertions(+)
create mode 100644 Documentation/devicetree/bindings/pwm/spear-pwm.txt
create mode 100644 drivers/pwm/pwm-spear.c

diff --git a/Documentation/devicetree/bindings/pwm/spear-pwm.txt b/Documentation/devicetree/bindings/pwm/spear-pwm.txt
new file mode 100644
index 0000000..3ac779d
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/spear-pwm.txt
@@ -0,0 +1,18 @@
+== ST SPEAr SoC PWM controller ==
+
+Required properties:
+- compatible: should be one of:
+ - "st,spear320-pwm"
+ - "st,spear1340-pwm"
+- reg: physical base address and length of the controller's registers
+- #pwm-cells: number of cells used to specify PWM which is fixed to 2 on
+ SPEAr. The first cell specifies the per-chip index of the PWM to use and
+ the second cell is the period in nanoseconds.
+
+Example:
+
+ pwm: pwm@a8000000 {
+ compatible ="st,spear320-pwm";
+ reg = <0xa8000000 0x1000>;
+ #pwm-cells = <2>;
+ };
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index ed81720..6e556c7 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -112,6 +112,17 @@ config PWM_SAMSUNG
To compile this driver as a module, choose M here: the module
will be called pwm-samsung.

+config PWM_SPEAR
+ tristate "STMicroelectronics SPEAr PWM support"
+ depends on PLAT_SPEAR
+ depends on OF
+ help
+ Generic PWM framework driver for the PWM controller on ST
+ SPEAr SoCs.
+
+ To compile this driver as a module, choose M here: the module
+ will be called pwm-spear.
+
config PWM_TEGRA
tristate "NVIDIA Tegra PWM support"
depends on ARCH_TEGRA
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index acfe482..3b3f4c9a 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_PWM_MXS) += pwm-mxs.o
obj-$(CONFIG_PWM_PUV3) += pwm-puv3.o
obj-$(CONFIG_PWM_PXA) += pwm-pxa.o
obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o
+obj-$(CONFIG_PWM_SPEAR) += pwm-spear.o
obj-$(CONFIG_PWM_TEGRA) += pwm-tegra.o
obj-$(CONFIG_PWM_TIECAP) += pwm-tiecap.o
obj-$(CONFIG_PWM_TIEHRPWM) += pwm-tiehrpwm.o
diff --git a/drivers/pwm/pwm-spear.c b/drivers/pwm/pwm-spear.c
new file mode 100644
index 0000000..35124a01
--- /dev/null
+++ b/drivers/pwm/pwm-spear.c
@@ -0,0 +1,273 @@
+/*
+ * ST Microelectronics SPEAr Pulse Width Modulator driver
+ *
+ * Copyright (C) 2012 ST Microelectronics
+ * Shiraz Hashim <shiraz.hashim@st.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/err.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/kernel.h>
+#include <linux/math64.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#define NUM_PWM 4
+
+/* PWM registers and bits definitions */
+#define PWMCR 0x00 /* Control Register */
+#define PWMCR_PWM_ENABLE 0x1
+#define PWMCR_PRESCALE_SHIFT 2
+#define PWMCR_MIN_PRESCALE 0x00
+#define PWMCR_MAX_PRESCALE 0x3FFF
+
+#define PWMDCR 0x04 /* Duty Cycle Register */
+#define PWMDCR_MIN_DUTY 0x0001
+#define PWMDCR_MAX_DUTY 0xFFFF
+
+#define PWMPCR 0x08 /* Period Register */
+#define PWMPCR_MIN_PERIOD 0x0001
+#define PWMPCR_MAX_PERIOD 0xFFFF
+
+/* Following only available on 13xx SoCs */
+#define PWMMCR 0x3C /* Master Control Register */
+#define PWMMCR_PWM_ENABLE 0x1
+
+/**
+ * struct spear_pwm_chip - struct representing pwm chip
+ *
+ * @mmio_base: base address of pwm chip
+ * @clk: pointer to clk structure of pwm chip
+ * @chip: linux pwm chip representation
+ * @dev: pointer to device structure of pwm chip
+ */
+struct spear_pwm_chip {
+ void __iomem *mmio_base;
+ struct clk *clk;
+ struct pwm_chip chip;
+ struct device *dev;
+};
+
+static inline struct spear_pwm_chip *to_spear_pwm_chip(struct pwm_chip *chip)
+{
+ return container_of(chip, struct spear_pwm_chip, chip);
+}
+
+static inline u32 spear_pwm_readl(struct spear_pwm_chip *chip, unsigned int num,
+ unsigned long offset)
+{
+ return readl_relaxed(chip->mmio_base + (num << 4) + offset);
+}
+
+static inline void spear_pwm_writel(struct spear_pwm_chip *chip,
+ unsigned int num, unsigned long offset,
+ unsigned long val)
+{
+ writel_relaxed(val, chip->mmio_base + (num << 4) + offset);
+}
+
+int spear_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, int duty_ns,
+ int period_ns)
+{
+ struct spear_pwm_chip *pc = to_spear_pwm_chip(chip);
+ u64 val, div, clk_rate;
+ unsigned long prescale = PWMCR_MIN_PRESCALE, pv, dc;
+ int ret;
+
+ /*
+ * Find pv, dc and prescale to suit duty_ns and period_ns. This is done
+ * according to formulas described below:
+ *
+ * period_ns = 10^9 * (PRESCALE + 1) * PV / PWM_CLK_RATE
+ * duty_ns = 10^9 * (PRESCALE + 1) * DC / PWM_CLK_RATE
+ *
+ * PV = (PWM_CLK_RATE * period_ns) / (10^9 * (PRESCALE + 1))
+ * DC = (PWM_CLK_RATE * duty_ns) / (10^9 * (PRESCALE + 1))
+ */
+ clk_rate = clk_get_rate(pc->clk);
+ while (1) {
+ div = 1000000000;
+ div *= 1 + prescale;
+ val = clk_rate * period_ns;
+ pv = div64_u64(val, div);
+ val = clk_rate * duty_ns;
+ dc = div64_u64(val, div);
+
+ /* if duty_ns and period_ns are not achievable then return */
+ if (pv < PWMPCR_MIN_PERIOD || dc < PWMDCR_MIN_DUTY)
+ return -EINVAL;
+
+ /*
+ * if pv and dc have crossed their upper limit, then increase
+ * prescale and recalculate pv and dc.
+ */
+ if (pv > PWMPCR_MAX_PERIOD || dc > PWMDCR_MAX_DUTY) {
+ if (++prescale > PWMCR_MAX_PRESCALE)
+ return -EINVAL;
+ continue;
+ }
+ break;
+ }
+
+ /*
+ * NOTE: the clock to PWM has to be enabled first before writing to the
+ * registers.
+ */
+ ret = clk_enable(pc->clk);
+ if (ret)
+ return ret;
+
+ spear_pwm_writel(pc, pwm->hwpwm, PWMCR,
+ prescale << PWMCR_PRESCALE_SHIFT);
+ spear_pwm_writel(pc, pwm->hwpwm, PWMDCR, dc);
+ spear_pwm_writel(pc, pwm->hwpwm, PWMPCR, pv);
+ clk_disable(pc->clk);
+
+ return 0;
+}
+
+static int spear_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct spear_pwm_chip *pc = to_spear_pwm_chip(chip);
+ int rc = 0;
+ u32 val;
+
+ rc = clk_enable(pc->clk);
+ if (rc < 0)
+ return rc;
+
+ val = spear_pwm_readl(pc, pwm->hwpwm, PWMCR);
+ val |= PWMCR_PWM_ENABLE;
+ spear_pwm_writel(pc, pwm->hwpwm, PWMCR, val);
+
+ return 0;
+}
+
+static void spear_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct spear_pwm_chip *pc = to_spear_pwm_chip(chip);
+ u32 val;
+
+ val = spear_pwm_readl(pc, pwm->hwpwm, PWMCR);
+ val &= ~PWMCR_PWM_ENABLE;
+ spear_pwm_writel(pc, pwm->hwpwm, PWMCR, val);
+
+ clk_disable(pc->clk);
+}
+
+static const struct pwm_ops spear_pwm_ops = {
+ .config = spear_pwm_config,
+ .enable = spear_pwm_enable,
+ .disable = spear_pwm_disable,
+ .owner = THIS_MODULE,
+};
+
+static int spear_pwm_probe(struct platform_device *pdev)
+{
+ struct device_node *np = pdev->dev.of_node;
+ struct spear_pwm_chip *pc;
+ struct resource *r;
+ int ret;
+ u32 val;
+
+ r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+ if (!r) {
+ dev_err(&pdev->dev, "no memory resources defined\n");
+ return -ENODEV;
+ }
+
+ pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
+ if (!pc) {
+ dev_err(&pdev->dev, "failed to allocate memory\n");
+ return -ENOMEM;
+ }
+
+ pc->mmio_base = devm_request_and_ioremap(&pdev->dev, r);
+ if (!pc->mmio_base)
+ return -EADDRNOTAVAIL;
+
+ pc->clk = devm_clk_get(&pdev->dev, NULL);
+ if (IS_ERR(pc->clk))
+ return PTR_ERR(pc->clk);
+
+ pc->dev = &pdev->dev;
+ platform_set_drvdata(pdev, pc);
+
+ pc->chip.dev = &pdev->dev;
+ pc->chip.ops = &spear_pwm_ops;
+ pc->chip.base = -1;
+ pc->chip.npwm = NUM_PWM;
+
+ ret = pwmchip_add(&pc->chip);
+ if (ret < 0) {
+ dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
+ return ret;
+ }
+
+ ret = clk_prepare_enable(pc->clk);
+ if (ret < 0)
+ return pwmchip_remove(&pc->chip);
+
+ if (of_device_is_compatible(np, "st,spear1340-pwm")) {
+ /*
+ * Following enables PWM chip, channels would still be
+ * enabled individually through their control register
+ */
+ val = readl_relaxed(pc->mmio_base + PWMMCR);
+ val |= PWMMCR_PWM_ENABLE;
+ writel_relaxed(val, pc->mmio_base + PWMMCR);
+
+ }
+
+ /* only disable the clk and leave it prepared */
+ clk_disable(pc->clk);
+
+ return 0;
+}
+
+static int spear_pwm_remove(struct platform_device *pdev)
+{
+ struct spear_pwm_chip *pc = platform_get_drvdata(pdev);
+ int i;
+
+ for (i = 0; i < NUM_PWM; i++)
+ pwm_disable(&pc->chip.pwms[i]);
+
+ /* clk was prepared in probe, hence unprepare it here */
+ clk_unprepare(pc->clk);
+ return pwmchip_remove(&pc->chip);
+}
+
+static struct of_device_id spear_pwm_of_match[] = {
+ { .compatible = "st,spear320-pwm" },
+ { .compatible = "st,spear1340-pwm" },
+ { }
+};
+
+MODULE_DEVICE_TABLE(of, spear_pwm_of_match);
+
+static struct platform_driver spear_pwm_driver = {
+ .driver = {
+ .name = "spear-pwm",
+ .of_match_table = spear_pwm_of_match,
+ },
+ .probe = spear_pwm_probe,
+ .remove = spear_pwm_remove,
+};
+
+module_platform_driver(spear_pwm_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Shiraz Hashim <shiraz.hashim@st.com>");
+MODULE_AUTHOR("Viresh Kumar <viresh.kumar@linaro.com>");
+MODULE_ALIAS("platform:spear-pwm");
--
1.7.10