hwrng: meson - add support for 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 <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/char/hw_random/meson-rng.c

···
 #include <linux/types.h>
 #include <linux/of.h>
 #include <linux/clk.h>
+#include <linux/iopoll.h>
 
-#define RNG_DATA 0x00
+#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 {
+	int (*read)(struct hwrng *rng, void *buf, size_t max, bool wait);
+};
 
 struct meson_rng_data {
 	void __iomem *base;
 	struct hwrng rng;
+	struct device *dev;
 };
 
 static int meson_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
···
 	return sizeof(u32);
 }
 
+static int meson_rng_wait_status(void __iomem *cfg_addr, int bit)
+{
+	u32 status = 0;
+	int ret;
+
+	ret = readl_relaxed_poll_timeout_atomic(cfg_addr,
+						status, !(status & bit),
+						10, 10000);
+	if (ret)
+		return -EBUSY;
+
+	return 0;
+}
+
+static int meson_s4_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	struct meson_rng_data *data =
+			container_of(rng, struct meson_rng_data, rng);
+
+	void __iomem *cfg_addr = data->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) {
+		dev_err(data->dev, "Seed isn't ready, try again\n");
+		return err;
+	}
+
+	err = meson_rng_wait_status(cfg_addr, RUN_BIT);
+	if (err) {
+		dev_err(data->dev, "Can't get random number, try again\n");
+		return err;
+	}
+
+	*(u32 *)buf = readl_relaxed(data->base + RNG_S4_DATA);
+
+	return sizeof(u32);
+}
+
 static int meson_rng_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct meson_rng_data *data;
 	struct clk *core_clk;
+	const struct meson_rng_priv *priv;
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
+
+	priv = device_get_match_data(&pdev->dev);
+	if (!priv)
+		return -ENODEV;
 
 	data->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(data->base))
···
 				     "Failed to get core clock\n");
 
 	data->rng.name = pdev->name;
-	data->rng.read = meson_rng_read;
+	data->rng.read = priv->read;
+
+	data->dev = &pdev->dev;
 
 	return devm_hwrng_register(dev, &data->rng);
 }
 
+static const struct meson_rng_priv meson_rng_priv = {
+	.read = meson_rng_read,
+};
+
+static const struct meson_rng_priv meson_rng_priv_s4 = {
+	.read = meson_s4_rng_read,
+};
+
 static const struct of_device_id meson_rng_of_match[] = {
-	{ .compatible = "amlogic,meson-rng", },
+	{
+		.compatible = "amlogic,meson-rng",
+		.data = (void *)&meson_rng_priv,
+	},
+	{
+		.compatible = "amlogic,meson-s4-rng",
+		.data = (void *)&meson_rng_priv_s4,
+	},
 	{},
 };
 MODULE_DEVICE_TABLE(of, meson_rng_of_match);