[PATCH v2 2/2] pwm: Add support for Xilinx AXI Timer

[Sean Anderson]

This adds PWM support for Xilinx LogiCORE IP AXI soft timers commonly
found on Xilinx FPGAs. There is another driver for this device located
at arch/microblaze/kernel/timer.c, but it is only used for timekeeping.
This driver was written with reference to Xilinx DS764 for v1.03.a [1].

[1] https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf

Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>
---
I tried adding a XILINX_PWM_ prefix to all the defines, but IMO it
really hurt readability. That prefix almost doubles the size the
defines, and is particularly excessive in something like
XILINX_PWM_TCSR_RUN_MASK.

Changes in v2:
- Don't compile this module by default for arm64
- Add dependencies on COMMON_CLK and HAS_IOMEM
- Add comment explaining why we depend on !MICROBLAZE
- Add comment describing device
- Rename TCSR_(SET|CLEAR) to TCSR_RUN_(SET|CLEAR)
- Use NSEC_TO_SEC instead of defining our own
- Use TCSR_RUN_MASK to check if the PWM is enabled, as suggested by Uwe
- Cast dividends to u64 to avoid overflow
- Check for over- and underflow when calculating TLR
- Set xilinx_pwm_ops.owner
- Don't set pwmchip.base to -1
- Check range of xlnx,count-width
- Ensure the clock is always running when the pwm is registered
- Remove debugfs file :l
- Report errors with dev_error_probe

 drivers/pwm/Kconfig      |  13 ++
 drivers/pwm/Makefile     |   1 +
 drivers/pwm/pwm-xilinx.c | 301 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 315 insertions(+)
 create mode 100644 drivers/pwm/pwm-xilinx.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 8ae68d6203fb..b1ad77ec81e3 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -620,4 +620,17 @@ config PWM_VT8500
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-vt8500.
 
+config PWM_XILINX
+	tristate "Xilinx AXI Timer PWM support"
+	depends on HAS_IOMEM && COMMON_CLK
+	# This driver conflicts with arch/microblaze/kernel/timer.c
+	depends on !MICROBLAZE
+	help
+	  PWM framework driver for Xilinx LogiCORE IP AXI Timers. This
+	  timer is typically a soft core which may be present in Xilinx
+	  FPGAs. If you don't have this IP in your design, choose N.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-xilinx.
+
 endif
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index d43b1e17e8e1..655df169b895 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -58,3 +58,4 @@ obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o
 obj-$(CONFIG_PWM_TWL_LED)	+= pwm-twl-led.o
 obj-$(CONFIG_PWM_VISCONTI)	+= pwm-visconti.o
 obj-$(CONFIG_PWM_VT8500)	+= pwm-vt8500.o
+obj-$(CONFIG_PWM_XILINX)	+= pwm-xilinx.o
diff --git a/drivers/pwm/pwm-xilinx.c b/drivers/pwm/pwm-xilinx.c
new file mode 100644
index 000000000000..10483da1a942
--- /dev/null
+++ b/drivers/pwm/pwm-xilinx.c
@@ -0,0 +1,301 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2021 Sean Anderson <sean.anderson@xxxxxxxx>
+ *
+ * For Xilinx LogiCORE IP AXI Timer documentation, refer to DS764:
+ * https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf
+ *
+ * Hardware limitations:
+ * - When changing both duty cycle and period, we may end up with one cycle
+ *   with the old duty cycle and the new period.
+ * - Cannot produce 100% duty cycle.
+ * - Only produces "normal" output.
+ */
+#include <asm/io.h>
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+
+#define TCSR0	0x00
+#define TLR0	0x04
+#define TCR0	0x08
+#define TCSR1	0x10
+#define TLR1	0x14
+#define TCR1	0x18
+
+#define TCSR_MDT	BIT(0)
+#define TCSR_UDT	BIT(1)
+#define TCSR_GENT	BIT(2)
+#define TCSR_CAPT	BIT(3)
+#define TCSR_ARHT	BIT(4)
+#define TCSR_LOAD	BIT(5)
+#define TCSR_ENIT	BIT(6)
+#define TCSR_ENT	BIT(7)
+#define TCSR_TINT	BIT(8)
+#define TCSR_PWMA	BIT(9)
+#define TCSR_ENALL	BIT(10)
+#define TCSR_CASC	BIT(11)
+
+/*
+ * The idea here is to capture whether the PWM is actually running (e.g.
+ * because we or the bootloader set it up) and we need to be careful to ensure
+ * we don't cause a glitch. According to the device data sheet, to enable the
+ * PWM we need to
+ *
+ * - Set both timers to generate mode (MDT=1)
+ * - Set both timers to PWM mode (PWMA=1)
+ * - Enable the generate out signals (GENT=1)
+ *
+ * In addition,
+ *
+ * - The timer must be running (ENT=1)
+ * - The timer must auto-reload TLR into TCR (ARHT=1)
+ * - We must not be in the process of loading TLR into TCR (LOAD=0)
+ * - Cascade mode must be disabled (CASC=0)
+ *
+ * If any of these differ from usual, then the PWM is either disabled, or is
+ * running in a mode that this driver does not support.
+ */
+#define TCSR_RUN_SET (TCSR_GENT | TCSR_ARHT | TCSR_ENT | TCSR_PWMA)
+#define TCSR_RUN_CLEAR (TCSR_MDT | TCSR_LOAD)
+#define TCSR_RUN_MASK (TCSR_RUN_SET | TCSR_RUN_CLEAR)
+
+/**
+ * struct xilinx_pwm_device - Driver data for Xilinx AXI timer PWM driver
+ * @chip: PWM controller chip
+ * @clk: Parent clock
+ * @regs: Base address of this device
+ * @width: Width of the counters, in bits
+ */
+struct xilinx_pwm_device {
+	struct pwm_chip chip;
+	struct clk *clk;
+	void __iomem *regs;
+	unsigned int width;
+};
+
+static inline struct xilinx_pwm_device *xilinx_pwm_chip_to_device(struct pwm_chip *chip)
+{
+	return container_of(chip, struct xilinx_pwm_device, chip);
+}
+
+static bool xilinx_pwm_is_enabled(u32 tcsr0, u32 tcsr1)
+{
+	return ((TCSR_RUN_MASK | TCSR_CASC) & tcsr0) == TCSR_RUN_SET &&
+		(TCSR_RUN_MASK & tcsr1) == TCSR_RUN_SET;
+}
+
+static int xilinx_pwm_calc_tlr(struct xilinx_pwm_device *pwm, u32 *tlr, u32 tcsr,
+			       unsigned int period)
+{
+	u64 max_count = BIT_ULL(pwm->width) - 1;
+	u64 cycles = DIV_ROUND_DOWN_ULL((u64)period * clk_get_rate(pwm->clk),
+					NSEC_PER_SEC);
+
+	if (cycles < 2)
+		return -ERANGE;
+
+	if (tcsr & TCSR_UDT) {
+		if (cycles - 2 > max_count)
+			return -ERANGE;
+		*tlr = cycles - 2;
+	} else {
+		if (cycles > max_count + 2)
+			return -ERANGE;
+		*tlr = max_count - cycles + 2;
+	}
+
+	return 0;
+}
+
+static unsigned int xilinx_pwm_get_period(struct xilinx_pwm_device *pwm,
+					  u32 tlr, u32 tcsr)
+{
+	u64 cycles;
+
+	if (tcsr & TCSR_UDT)
+		cycles = tlr + 2;
+	else
+		cycles = (BIT_ULL(pwm->width) - 1) - tlr + 2;
+
+	return DIV_ROUND_UP_ULL(cycles * NSEC_PER_SEC, clk_get_rate(pwm->clk));
+}
+
+static int xilinx_pwm_apply(struct pwm_chip *chip, struct pwm_device *unused,
+			    const struct pwm_state *state)
+{
+	int ret;
+	struct xilinx_pwm_device *pwm = xilinx_pwm_chip_to_device(chip);
+	u32 tlr0, tlr1;
+	u32 tcsr0 = readl(pwm->regs + TCSR0);
+	u32 tcsr1 = readl(pwm->regs + TCSR1);
+	bool enabled = xilinx_pwm_is_enabled(tcsr0, tcsr1);
+
+	if (state->polarity != PWM_POLARITY_NORMAL)
+		return -EINVAL;
+
+	ret = xilinx_pwm_calc_tlr(pwm, &tlr0, tcsr0, state->period);
+	if (ret)
+		return ret;
+
+	ret = xilinx_pwm_calc_tlr(pwm, &tlr1, tcsr1, state->duty_cycle);
+	if (ret)
+		return ret;
+
+	if (!enabled && state->enabled)
+		clk_rate_exclusive_get(pwm->clk);
+
+	writel(tlr0, pwm->regs + TLR0);
+	writel(tlr1, pwm->regs + TLR1);
+
+	if (state->enabled) {
+		/* Only touch the TCSRs if we aren't already running */
+		if (!enabled) {
+			/* Load TLR into TCR */
+			writel(tcsr0 | TCSR_LOAD, pwm->regs + TCSR0);
+			writel(tcsr1 | TCSR_LOAD, pwm->regs + TCSR1);
+			/* Enable timers all at once with ENALL */
+			tcsr0 = (TCSR_RUN_SET & ~TCSR_ENT) | (tcsr0 & TCSR_UDT);
+			tcsr1 = TCSR_RUN_SET | TCSR_ENALL | (tcsr1 & TCSR_UDT);
+			writel(tcsr0, pwm->regs + TCSR0);
+			writel(tcsr1, pwm->regs + TCSR1);
+		}
+	} else {
+		writel(tcsr0 & ~TCSR_RUN_SET, pwm->regs + TCSR0);
+		writel(tcsr1 & ~TCSR_RUN_SET, pwm->regs + TCSR1);
+	}
+
+	if (enabled && !state->enabled)
+		clk_rate_exclusive_put(pwm->clk);
+
+	return 0;
+}
+
+static void xilinx_pwm_get_state(struct pwm_chip *chip,
+				 struct pwm_device *unused,
+				 struct pwm_state *state)
+{
+	struct xilinx_pwm_device *pwm = xilinx_pwm_chip_to_device(chip);
+	u32 tlr0, tlr1, tcsr0, tcsr1;
+
+	tlr0 = readl(pwm->regs + TLR0);
+	tlr1 = readl(pwm->regs + TLR1);
+	tcsr0 = readl(pwm->regs + TCSR0);
+	tcsr1 = readl(pwm->regs + TCSR1);
+
+	state->period = xilinx_pwm_get_period(pwm, tlr0, tcsr0);
+	state->duty_cycle = xilinx_pwm_get_period(pwm, tlr1, tcsr1);
+	state->enabled = xilinx_pwm_is_enabled(tcsr0, tcsr1);
+	state->polarity = PWM_POLARITY_NORMAL;
+}
+
+static const struct pwm_ops xilinx_pwm_ops = {
+	.apply = xilinx_pwm_apply,
+	.get_state = xilinx_pwm_get_state,
+	.owner = THIS_MODULE,
+};
+
+static int xilinx_pwm_probe(struct platform_device *pdev)
+{
+	bool enabled = false;
+	int i, ret;
+	struct device *dev = &pdev->dev;
+	struct xilinx_pwm_device *pwm;
+	u32 one_timer;
+
+	ret = of_property_read_u32(dev->of_node, "xlnx,one-timer-only",
+				   &one_timer);
+	if (ret || one_timer)
+		return dev_err_probe(dev, -EINVAL,
+				     "two timers are needed for PWM mode\n");
+
+	for (i = 0; i < 2; i++) {
+		char fmt[] = "xlnx,gen%u-assert";
+		char buf[sizeof(fmt)];
+		u32 gen;
+
+		snprintf(buf, sizeof(buf), fmt, i);
+		ret = of_property_read_u32(dev->of_node, buf, &gen);
+		if (ret || !gen)
+			return dev_err_probe(dev, -EINVAL,
+					     "generateout%u must be active high\n",
+					     i);
+	}
+
+	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
+	if (!pwm)
+		return -ENOMEM;
+	platform_set_drvdata(pdev, pwm);
+
+	pwm->chip.dev = &pdev->dev;
+	pwm->chip.ops = &xilinx_pwm_ops;
+	pwm->chip.npwm = 1;
+
+	pwm->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(pwm->regs))
+		return PTR_ERR(pwm->regs);
+
+	ret = of_property_read_u32(dev->of_node, "xlnx,count-width", &pwm->width);
+	if (ret || pwm->width < 8 || pwm->width > 32)
+		return dev_err_probe(dev, -EINVAL,
+				     "missing or invalid counter width\n");
+
+	pwm->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(pwm->clk))
+		return dev_err_probe(dev, PTR_ERR(pwm->clk), "missing clock\n");
+
+	ret = clk_prepare_enable(pwm->clk);
+	if (ret)
+		return dev_err_probe(dev, ret, "clock enable failed\n");
+
+	enabled = xilinx_pwm_is_enabled(readl(pwm->regs + TCSR0),
+					readl(pwm->regs + TCSR1));
+	if (enabled)
+		clk_rate_exclusive_get(pwm->clk);
+
+	ret = pwmchip_add(&pwm->chip);
+	if (ret) {
+		dev_err_probe(dev, ret, "could not register pwm chip\n");
+		if (enabled)
+			clk_rate_exclusive_put(pwm->clk);
+		clk_disable_unprepare(pwm->clk);
+	}
+	return ret;
+}
+
+static int xilinx_pwm_remove(struct platform_device *pdev)
+{
+	struct xilinx_pwm_device *pwm = platform_get_drvdata(pdev);
+	bool enabled = xilinx_pwm_is_enabled(readl(pwm->regs + TCSR0),
+					     readl(pwm->regs + TCSR1));
+
+	pwmchip_remove(&pwm->chip);
+	if (enabled)
+		clk_rate_exclusive_put(pwm->clk);
+	clk_disable_unprepare(pwm->clk);
+
+	return 0;
+}
+
+static const struct of_device_id xilinx_pwm_of_match[] = {
+	{ .compatible = "xlnx,xps-timer-1.00.a" },
+	{ .compatible = "xlnx,axi-timer-2.0" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, xilinx_pwm_of_match);
+
+static struct platform_driver xilinx_pwm_driver = {
+	.probe = xilinx_pwm_probe,
+	.remove = xilinx_pwm_remove,
+	.driver = {
+		.name = "xilinx-pwm",
+		.of_match_table = of_match_ptr(xilinx_pwm_of_match),
+	},
+};
+module_platform_driver(xilinx_pwm_driver);
+
+MODULE_ALIAS("platform:xilinx-pwm");
+MODULE_DESCRIPTION("Xilinx LogiCORE IP AXI Timer PWM driver");
+MODULE_LICENSE("GPL v2");
-- 
2.25.1