drivers: rng: add support for Meson S4

For some Amlogic SOC's, mechanism to obtain random number
has been changed. For example, S4 now uses status bit waiting algo.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20231012075828.22685-2-avromanov@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

drivers/rng/meson-rng.c

@@ -10,10 +10,23 @@
 #include <dm.h>
 #include <rng.h>
 #include <asm/io.h>
+#include <linux/iopoll.h>
+
+#define RNG_DATA	0x00
+#define RNG_S4_DATA	0x08
+#define RNG_S4_CFG	0x00
+
+#define RUN_BIT		BIT(0)
+#define SEED_READY_STS_BIT	BIT(31)
+
+struct meson_rng_priv {
+	u32 (*read)(fdt_addr_t base);
+};
 
 struct meson_rng_plat {
 	fdt_addr_t base;
 	struct clk clk;
+	struct meson_rng_priv *priv;
 };
 
 /**
@@ -27,10 +40,11 @@ struct meson_rng_plat {
 static int meson_rng_read(struct udevice *dev, void *data, size_t len)
 {
 	struct meson_rng_plat *pdata = dev_get_plat(dev);
+	struct meson_rng_priv *priv = pdata->priv;
 	char *buffer = (char *)data;
 
 	while (len) {
-		u32 rand = readl(pdata->base);
+		u32 rand = priv->read(pdata->base);
 		size_t step;
 
 		if (len >= 4)
@@ -44,6 +58,47 @@ static int meson_rng_read(struct udevice *dev, void *data, size_t len)
 	return 0;
 }
 
+static int meson_rng_wait_status(void __iomem *cfg_addr, int bit)
+{
+	u32 status = 0;
+	int ret;
+
+	ret = readl_relaxed_poll_timeout(cfg_addr,
+					 status, !(status & bit),
+					 10000);
+	if (ret)
+		return -EBUSY;
+
+	return 0;
+}
+
+static u32 meson_common_rng_read(fdt_addr_t base)
+{
+	return readl(base);
+}
+
+static u32 meson_s4_rng_read(fdt_addr_t base)
+{
+	void __iomem *cfg_addr = (void *)base + RNG_S4_CFG;
+	int err;
+
+	writel_relaxed(readl_relaxed(cfg_addr) | SEED_READY_STS_BIT, cfg_addr);
+
+	err = meson_rng_wait_status(cfg_addr, SEED_READY_STS_BIT);
+	if (err) {
+		pr_err("Seed isn't ready, try again\n");
+		return err;
+	}
+
+	err = meson_rng_wait_status(cfg_addr, RUN_BIT);
+	if (err) {
+		pr_err("Can't get random number, try again\n");
+		return err;
+	}
+
+	return readl_relaxed(base + RNG_S4_DATA);
+}
+
 /**
  * meson_rng_probe() - probe rng device
  *
@@ -59,6 +114,8 @@ static int meson_rng_probe(struct udevice *dev)
 	if (err)
 		return err;
 
+	pdata->priv = (struct meson_rng_priv *)dev_get_driver_data(dev);
+
 	return 0;
 }
 
@@ -102,9 +159,22 @@ static const struct dm_rng_ops meson_rng_ops = {
 	.read = meson_rng_read,
 };
 
+static const struct meson_rng_priv meson_rng_priv = {
+	.read = meson_common_rng_read,
+};
+
+static const struct meson_rng_priv meson_rng_priv_s4 = {
+	.read = meson_s4_rng_read,
+};
+
 static const struct udevice_id meson_rng_match[] = {
 	{
 		.compatible = "amlogic,meson-rng",
+		.data = (ulong)&meson_rng_priv,
+	},
+	{
+		.compatible = "amlogic,meson-s4-rng",
+		.data = (ulong)&meson_rng_priv_s4,
 	},
 	{},
 };