timer: imx-gpt: Add timer support for i.MX SoCs family

This timer driver uses GPT Timer (General Purpose Timer) available on
a lot of i.MX SoCs family. This driver deals with both 24Mhz oscillator
as well as peripheral clock.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
[Giulio: added the driver's stub and handled peripheral clock prescaler
setting making driver to work correctly]
Signed-off-by: Jesse Taube <mr.bossman075@gmail.com>
[Jesse: added init, setting prescaler for 24Mhz support and enabling
timer]

drivers/timer/Kconfig

@@ -227,4 +227,11 @@ config MCHP_PIT64B_TIMER
 	  Select this to enable support for Microchip 64-bit periodic
 	  interval timer.
 
+config IMX_GPT_TIMER
+	bool "NXP i.MX GPT timer support"
+	depends on TIMER
+	help
+	  Select this to enable support for the timer found on
+	  NXP i.MX devices.
+
 endmenu

drivers/timer/Makefile

@@ -25,3 +25,4 @@ obj-$(CONFIG_STM32_TIMER)	+= stm32_timer.o
 obj-$(CONFIG_X86_TSC_TIMER)	+= tsc_timer.o
 obj-$(CONFIG_MTK_TIMER)		+= mtk_timer.o
 obj-$(CONFIG_MCHP_PIT64B_TIMER)	+= mchp-pit64b-timer.o
+obj-$(CONFIG_IMX_GPT_TIMER)	+= imx-gpt-timer.o

drivers/timer/imx-gpt-timer.c

@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2021
+ * Author(s): Giulio Benetti <giulio.benetti@benettiengineering.com>
+ */
+
+#include <common.h>
+#include <clk.h>
+#include <dm.h>
+#include <fdtdec.h>
+#include <timer.h>
+#include <dm/device_compat.h>
+
+#include <asm/io.h>
+
+#define GPT_CR_EN			BIT(0)
+#define GPT_CR_FRR			BIT(9)
+#define GPT_CR_EN_24M			BIT(10)
+#define GPT_CR_SWR			BIT(15)
+
+#define GPT_PR_PRESCALER24M_MASK	0x0000F000
+#define GPT_PR_PRESCALER24M_SHIFT	12
+#define GPT_PR_PRESCALER24M_MAX	(GPT_PR_PRESCALER24M_MASK >> GPT_PR_PRESCALER24M_SHIFT)
+#define GPT_PR_PRESCALER_MASK		0x00000FFF
+#define GPT_PR_PRESCALER_SHIFT		0
+#define GPT_PR_PRESCALER_MAX		(GPT_PR_PRESCALER_MASK >> GPT_PR_PRESCALER_SHIFT)
+
+#define GPT_CLKSRC_IPG_CLK		(1 << 6)
+#define GPT_CLKSRC_IPG_CLK_24M		(5 << 6)
+
+/* If CONFIG_SYS_HZ_CLOCK not specified et's default to 3Mhz */
+#ifndef CONFIG_SYS_HZ_CLOCK
+#define CONFIG_SYS_HZ_CLOCK		3000000
+#endif
+
+struct imx_gpt_timer_regs {
+	u32 cr;
+	u32 pr;
+	u32 sr;
+	u32 ir;
+	u32 ocr1;
+	u32 ocr2;
+	u32 ocr3;
+	u32 icr1;
+	u32 icr2;
+	u32 cnt;
+};
+
+struct imx_gpt_timer_priv {
+	struct imx_gpt_timer_regs *base;
+};
+
+static u64 imx_gpt_timer_get_count(struct udevice *dev)
+{
+	struct imx_gpt_timer_priv *priv = dev_get_priv(dev);
+	struct imx_gpt_timer_regs *regs = priv->base;
+
+	return timer_conv_64(readl(&regs->cnt));
+}
+
+static int imx_gpt_setup(struct imx_gpt_timer_regs *regs, u32 rate)
+{
+	u32 prescaler = (rate / CONFIG_SYS_HZ_CLOCK) - 1;
+
+	/* Reset the timer */
+	setbits_le32(&regs->cr, GPT_CR_SWR);
+
+	/* Wait for timer to finish reset */
+	while (readl(&regs->cr) & GPT_CR_SWR)
+		;
+
+	if (rate == 24000000UL) {
+		/* Set timer frequency if using 24M clock source */
+		if (prescaler > GPT_PR_PRESCALER24M_MAX)
+			return -EINVAL;
+
+		/* Set 24M prescaler */
+		writel((prescaler << GPT_PR_PRESCALER24M_SHIFT), &regs->pr);
+		/* Set Oscillator as clock source, enable 24M input and set gpt
+		 * in free-running mode
+		 */
+		writel(GPT_CLKSRC_IPG_CLK_24M | GPT_CR_EN_24M | GPT_CR_FRR, &regs->cr);
+	} else {
+		if (prescaler > GPT_PR_PRESCALER_MAX)
+			return -EINVAL;
+
+		/* Set prescaler */
+		writel((prescaler << GPT_PR_PRESCALER_SHIFT), &regs->pr);
+		/* Set Peripheral as clock source and set gpt in free-running
+		 * mode
+		 */
+		writel(GPT_CLKSRC_IPG_CLK | GPT_CR_FRR, &regs->cr);
+	}
+
+	/* Start timer */
+	setbits_le32(&regs->cr, GPT_CR_EN);
+
+	return 0;
+}
+
+static int imx_gpt_timer_probe(struct udevice *dev)
+{
+	struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
+	struct imx_gpt_timer_priv *priv = dev_get_priv(dev);
+	struct imx_gpt_timer_regs *regs;
+	struct clk clk;
+	fdt_addr_t addr;
+	u32 clk_rate;
+	int ret;
+
+	addr = dev_read_addr(dev);
+	if (addr == FDT_ADDR_T_NONE)
+		return -EINVAL;
+
+	priv->base = (struct imx_gpt_timer_regs *)addr;
+	regs = priv->base;
+
+	ret = clk_get_by_index(dev, 0, &clk);
+	if (ret < 0)
+		return ret;
+
+	ret = clk_enable(&clk);
+	if (ret) {
+		dev_err(dev, "Failed to enable clock\n");
+		return ret;
+	}
+
+	/* Get timer clock rate */
+	clk_rate = clk_get_rate(&clk);
+	if (clk_rate <= 0) {
+		dev_err(dev, "Could not get clock rate...\n");
+		return -EINVAL;
+	}
+
+	ret = imx_gpt_setup(regs, clk_rate);
+	if (ret) {
+		dev_err(dev, "Could not setup timer\n");
+		return ret;
+	}
+
+	uc_priv->clock_rate = CONFIG_SYS_HZ_CLOCK;
+
+	return 0;
+}
+
+static const struct timer_ops imx_gpt_timer_ops = {
+	.get_count = imx_gpt_timer_get_count,
+};
+
+static const struct udevice_id imx_gpt_timer_ids[] = {
+	{ .compatible = "fsl,imxrt-gpt" },
+	{}
+};
+
+U_BOOT_DRIVER(imx_gpt_timer) = {
+	.name = "imx_gpt_timer",
+	.id = UCLASS_TIMER,
+	.of_match = imx_gpt_timer_ids,
+	.priv_auto = sizeof(struct imx_gpt_timer_priv),
+	.probe = imx_gpt_timer_probe,
+	.ops = &imx_gpt_timer_ops,
+};