[PATCH v1 1/3] drivers: rng: add check status bit feature

[Alexey Romanov <avromanov@sberdevices.ru>]

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@sberdevices.ru>
---
 drivers/char/hw_random/meson-rng.c | 77 ++++++++++++++++++++++++++++--
 1 file changed, 74 insertions(+), 3 deletions(-)

diff --git a/drivers/char/hw_random/meson-rng.c b/drivers/char/hw_random/meson-rng.c
index a4eb8e35f13d..c6d7349630a1 100644
--- a/drivers/char/hw_random/meson-rng.c
+++ b/drivers/char/hw_random/meson-rng.c
@@ -14,19 +14,65 @@
 #include <linux/of.h>
 #include <linux/clk.h>
 
-#define RNG_DATA 0x00
+struct meson_rng_priv {
+	bool check_status_bit;
+	unsigned int data_offset;
+	unsigned int cfg_offset;
+};
 
 struct meson_rng_data {
 	void __iomem *base;
 	struct hwrng rng;
+	struct device *dev;
+	const struct meson_rng_priv *priv;
 };
 
+#define RUN_BIT			0
+#define SEED_READY_STS_BIT	31
+#define RETRY_CNT		100
+
+static int meson_rng_wait_status(void __iomem *cfg_addr, int bit)
+{
+	u32 status;
+	u32 cnt = 0;
+
+	do {
+		status = readl_relaxed(cfg_addr) & BIT(bit);
+		cpu_relax();
+	} while (status && (cnt++ < RETRY_CNT));
+
+	if (status)
+		return -EBUSY;
+
+	return 0;
+}
+
 static int meson_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);
+	const struct meson_rng_priv *priv = data->priv;
+
+	if (priv->check_status_bit) {
+		void __iomem *cfg_addr = data->base + priv->cfg_offset;
+		int err;
+
+		writel_relaxed(readl_relaxed(cfg_addr) | BIT(SEED_READY_STS_BIT), cfg_addr);
 
-	*(u32 *)buf = readl_relaxed(data->base + RNG_DATA);
+		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 + priv->data_offset);
 
 	return sizeof(u32);
 }
@@ -41,6 +87,10 @@ static int meson_rng_probe(struct platform_device *pdev)
 	if (!data)
 		return -ENOMEM;
 
+	data->priv = device_get_match_data(&pdev->dev);
+	if (!data->priv)
+		return -ENODEV;
+
 	data->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(data->base))
 		return PTR_ERR(data->base);
@@ -53,11 +103,32 @@ static int meson_rng_probe(struct platform_device *pdev)
 	data->rng.name = pdev->name;
 	data->rng.read = meson_rng_read;
 
+	data->dev = &pdev->dev;
+
 	return devm_hwrng_register(dev, &data->rng);
 }
 
+static const struct meson_rng_priv meson_rng_priv = {
+	.check_status_bit = false,
+	.data_offset = 0x0,
+	.cfg_offset = 0x0,
+};
+
+static const struct meson_rng_priv meson_rng_priv_s4 = {
+	.check_status_bit = true,
+	.data_offset = 0x8,
+	.cfg_offset = 0x0,
+};
+
 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-rng-s4",
+		.data = (void *)&meson_rng_priv_s4,
+	},
 	{},
 };
 MODULE_DEVICE_TABLE(of, meson_rng_of_match);
-- 
2.38.1