[PATCH v5] timer: imx-gpt: Add timer support for i.MX SoCs family

[Jesse]

From: Jesse Taube <mr.bossman075 at gmail.com>

This timer driver is using GPT Timer (General Purpose Timer)
available on most i.MX SoCs.
Since this driver is only meant to provide u-boot's timer and counter,
and most of the i.MX* SoCs use a 24Mhz crystal, 
let's focus on that specific source.

Signed-off-by: Giulio Benetti <giulio.benetti at benettiengineering.com>
Signed-off-by: Jesse Taube <mr.bossman075 at gmail.com>

---
V1->V2:
* Fixed indentation
* Fixed capitals
* Made timer work on only 24MHz clock
V2->V3:
* Fixed indentation
* Made implementation imatate the Linux kernel
* Fix wrong definition
V3->V4:
* Fixed indentation
* Made bit manipluation into its own function.
V4->V5:
* Fixed indentation
* Made commit message 75 char 
* Moved prescaler code into sub funcions

 drivers/timer/Kconfig         |   7 ++
 drivers/timer/Makefile        |   1 +
 drivers/timer/imx-gpt-timer.c | 160 ++++++++++++++++++++++++++++++++++
 3 files changed, 168 insertions(+)
 create mode 100644 drivers/timer/imx-gpt-timer.c

diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index 80743a2551..ee81dfa776 100644
--- a/drivers/timer/Kconfig
+++ b/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
diff --git a/drivers/timer/Makefile b/drivers/timer/Makefile
index eb5c48cc6c..e214ba7268 100644
--- a/drivers/timer/Makefile
+++ b/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
diff --git a/drivers/timer/imx-gpt-timer.c b/drivers/timer/imx-gpt-timer.c
new file mode 100644
index 0000000000..1607a2fbcb
--- /dev/null
+++ b/drivers/timer/imx-gpt-timer.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020
+ * Author(s): Giulio Benetti <giulio.benetti at 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_SWR		0x00008000
+#define GPT_CR_EN_24M		0x00000400
+#define GPT_CR_EN		0x00000001
+#define GPT_PR_PRESCALER	0x00000FFF
+
+#define GPT_CLKSRC_IPG_CLK	(1 << 6)
+#define GPT_CLKSRC_IPG_CLK_24M	(5 << 6)
+
+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 readl(&regs->cnt);
+}
+
+static int imx_gpt_setup_24M(struct imx_gpt_timer_regs *regs)
+{
+	u32 prescaler;
+
+	/* Set timer frequency to 1MHz */
+	prescaler = (24000000UL / CONFIG_SYS_HZ_CLOCK) - 1;
+	if (prescaler > GPT_PR_PRESCALER)
+		return -EINVAL;
+	/* We set timer prescaler to obtain a 1MHz timer counter frequency */
+	writel(prescaler, &regs->pr);
+
+	writel(GPT_CLKSRC_IPG_CLK_24M | GPT_CR_EN_24M, &regs->cr);
+	return 0;
+}
+
+static int imx_gpt_setup_per(u32 rate, struct imx_gpt_timer_regs *regs)
+{
+	u32 prescaler;
+
+	/* Set timer frequency to 1MHz */
+	prescaler = (rate / CONFIG_SYS_HZ_CLOCK) - 1;
+	if (prescaler > GPT_PR_PRESCALER)
+		return -EINVAL;
+	/* We set timer prescaler to obtain a 1MHz timer counter frequency */
+	writel(prescaler, &regs->pr);
+
+	writel(GPT_CLKSRC_IPG_CLK, &regs->cr);
+	return 0;
+}
+
+static int imx_gpt_setup(u32 rate, struct imx_gpt_timer_regs *regs)
+{
+	int ret;
+
+	/* 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)
+		ret = imx_gpt_setup_per(rate, regs);
+	else
+		ret = imx_gpt_setup_24M(regs);
+
+	/* Start timer */
+	setbits_le32(&regs->cr, GPT_CR_EN);
+
+	return ret;
+}
+
+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 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;
+
+	uc_priv->clock_rate = CONFIG_SYS_HZ_CLOCK;
+
+	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 */
+	rate = clk_get_rate(&clk);
+	if (rate <= 0) {
+		dev_err(dev, "Could not get clock rate...\n");
+		return -EINVAL;
+	}
+
+	ret = imx_gpt_setup(rate, regs);
+	if (ret) {
+		dev_err(dev, "Could not setup timer\n");
+		return ret;
+	}
+	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,
+};
-- 
2.30.0