stm32mp1: rng: Add a driver for random number generator(rng) device

Add a driver for the rng device found on stm32mp1 platforms. The
driver provides a routine for reading the random number seed from the
hardware device.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Patrick Delaunay <patrick.delaunay@st.com>
Remove a superfluous blank line
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

drivers/rng/Kconfig

@@ -5,3 +5,10 @@ config DM_RNG
 	  Enable driver model for random number generator(rng) devices.
 	  This interface is used to initialise the rng device and to
 	  read the random seed from the device.
+
+config RNG_STM32MP1
+	bool "Enable random number generator for STM32MP1"
+	depends on ARCH_STM32MP && DM_RNG
+	default n
+	help
+	  Enable STM32MP1 rng driver.

drivers/rng/Makefile

@@ -4,3 +4,4 @@
 #
 
 obj-$(CONFIG_DM_RNG) += rng-uclass.o
+obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o

drivers/rng/stm32mp1_rng.c

@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2019, Linaro Limited
+ */
+
+#include <common.h>
+#include <clk.h>
+#include <dm.h>
+#include <reset.h>
+#include <rng.h>
+
+#include <asm/io.h>
+#include <linux/iopoll.h>
+#include <linux/kernel.h>
+
+#define RNG_CR 0x00
+#define RNG_CR_RNGEN BIT(2)
+#define RNG_CR_CED BIT(5)
+
+#define RNG_SR 0x04
+#define RNG_SR_SEIS BIT(6)
+#define RNG_SR_CEIS BIT(5)
+#define RNG_SR_SECS BIT(2)
+#define RNG_SR_DRDY BIT(0)
+
+#define RNG_DR 0x08
+
+struct stm32_rng_platdata {
+	fdt_addr_t base;
+	struct clk clk;
+	struct reset_ctl rst;
+};
+
+static int stm32_rng_read(struct udevice *dev, void *data, size_t len)
+{
+	int retval = 0, i;
+	u32 sr, count, reg;
+	size_t increment;
+	struct stm32_rng_platdata *pdata = dev_get_platdata(dev);
+
+	while (len > 0) {
+		retval = readl_poll_timeout(pdata->base + RNG_SR, sr,
+					    sr & RNG_SR_DRDY, 10000);
+		if (retval)
+			return retval;
+
+		if (sr & (RNG_SR_SEIS | RNG_SR_SECS)) {
+			/* As per SoC TRM */
+			clrbits_le32(pdata->base + RNG_SR, RNG_SR_SEIS);
+			for (i = 0; i < 12; i++)
+				readl(pdata->base + RNG_DR);
+			if (readl(pdata->base + RNG_SR) & RNG_SR_SEIS) {
+				printf("RNG Noise");
+				return -EIO;
+			}
+			/* start again */
+			continue;
+		}
+
+		/*
+		 * Once the DRDY bit is set, the RNG_DR register can
+		 * be read four consecutive times.
+		 */
+		count = 4;
+		while (len && count) {
+			reg = readl(pdata->base + RNG_DR);
+			memcpy(data, &reg, min(len, sizeof(u32)));
+			increment = min(len, sizeof(u32));
+			data += increment;
+			len -= increment;
+			count--;
+		}
+	}
+
+	return 0;
+}
+
+static int stm32_rng_init(struct stm32_rng_platdata *pdata)
+{
+	int err;
+
+	err = clk_enable(&pdata->clk);
+	if (err)
+		return err;
+
+	/* Disable CED */
+	writel(RNG_CR_RNGEN | RNG_CR_CED, pdata->base + RNG_CR);
+
+	/* clear error indicators */
+	writel(0, pdata->base + RNG_SR);
+
+	return 0;
+}
+
+static int stm32_rng_cleanup(struct stm32_rng_platdata *pdata)
+{
+	writel(0, pdata->base + RNG_CR);
+
+	return clk_disable(&pdata->clk);
+}
+
+static int stm32_rng_probe(struct udevice *dev)
+{
+	struct stm32_rng_platdata *pdata = dev_get_platdata(dev);
+
+	reset_assert(&pdata->rst);
+	udelay(20);
+	reset_deassert(&pdata->rst);
+
+	return stm32_rng_init(pdata);
+}
+
+static int stm32_rng_remove(struct udevice *dev)
+{
+	struct stm32_rng_platdata *pdata = dev_get_platdata(dev);
+
+	return stm32_rng_cleanup(pdata);
+}
+
+static int stm32_rng_ofdata_to_platdata(struct udevice *dev)
+{
+	struct stm32_rng_platdata *pdata = dev_get_platdata(dev);
+	int err;
+
+	pdata->base = dev_read_addr(dev);
+	if (!pdata->base)
+		return -ENOMEM;
+
+	err = clk_get_by_index(dev, 0, &pdata->clk);
+	if (err)
+		return err;
+
+	err = reset_get_by_index(dev, 0, &pdata->rst);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static const struct dm_rng_ops stm32_rng_ops = {
+	.read = stm32_rng_read,
+};
+
+static const struct udevice_id stm32_rng_match[] = {
+	{
+		.compatible = "st,stm32-rng",
+	},
+	{},
+};
+
+U_BOOT_DRIVER(stm32_rng) = {
+	.name = "stm32-rng",
+	.id = UCLASS_RNG,
+	.of_match = stm32_rng_match,
+	.ops = &stm32_rng_ops,
+	.probe = stm32_rng_probe,
+	.remove = stm32_rng_remove,
+	.platdata_auto_alloc_size = sizeof(struct stm32_rng_platdata),
+	.ofdata_to_platdata = stm32_rng_ofdata_to_platdata,
+};