[PATCH v6 3/3] hwrng: add a driver for Freescale RNGC

[Martin Kaiser <martin@kaiser.cx>]

The driver is ported from Freescale's Linux git and can be
found in the

	vendor/freescale/imx_2.6.35_maintain

branch.

The driver supports both RNG version C that's part of some Freescale
i.MX3 SoCs and version B that is available on i.MX2x chipsets.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
---
Changes in v6:
  - get rid of mxc: rename the .c file and the kconfig option
  - update the kconfig help text
  - rename structs, function names etc. from mxc_rngc to imx_rngc
  - rewrite the commit message to not use mxc
  - set myself as commit author so people know who to blame

Changes in v5:
  - use only one completion for self test and seeding

Changes in v4:
  - use readl, writel instead of the __raw versions
  - move the self test to a separate function
  - remove the error checks before the self test,
    it'll fail when there are errors
  - run the self test in the probe function, add a parameter to skip it
  - read the error status register before we clear irq and error
  - rewrite the irq handler to read and store error status
  - helper functions for irq mask, unmask
  - remove some more unused defines
  - fix a bounds check in the read function
  - read function: check status before the fifo level
  - clean up the file header, add myself to the copyright notice

Changes in v3:
   - use pdev->dev to request the irq, rngc->dev is not yet initialized
   - remove unused defines for registers and fields
   - use module_platform_driver_probe()
   - clean up the error handling in the probe function,
     disable the clock if necessary
   - self-test must succeed in the first run
   - check for errors after seeding, exit for errors unrelated to statistics
   - set a timeout when waiting for a completion

Changes in v2:
  - remove irq variable from private struct
  - move devm_request_irq from mxc_rngc_init to probe
  - return irq in case of error
  - handle irq 0 as error

 drivers/char/hw_random/Kconfig    |  14 ++
 drivers/char/hw_random/Makefile   |   1 +
 drivers/char/hw_random/imx-rngc.c | 331 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 346 insertions(+)
 create mode 100644 drivers/char/hw_random/imx-rngc.c

diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index 1b223c3..6530948 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -255,6 +255,20 @@ config HW_RANDOM_MXC_RNGA
 
 	  If unsure, say Y.
 
+config HW_RANDOM_IMX_RNGC
+	tristate "Freescale i.MX RNGC Random Number Generator"
+	depends on ARCH_MXC
+	default HW_RANDOM
+	---help---
+	  This driver provides kernel-side support for the Random Number
+	  Generator Version C hardware found on some Freescale i.MX
+	  processors. Version B is also supported by this driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called imx-rngc.
+
+	  If unsure, say Y.
+
 config HW_RANDOM_NOMADIK
 	tristate "ST-Ericsson Nomadik Random Number Generator support"
 	depends on ARCH_NOMADIK
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index b085975..39a67de 100644
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_HW_RANDOM_PASEMI) += pasemi-rng.o
 obj-$(CONFIG_HW_RANDOM_VIRTIO) += virtio-rng.o
 obj-$(CONFIG_HW_RANDOM_TX4939) += tx4939-rng.o
 obj-$(CONFIG_HW_RANDOM_MXC_RNGA) += mxc-rnga.o
+obj-$(CONFIG_HW_RANDOM_IMX_RNGC) += imx-rngc.o
 obj-$(CONFIG_HW_RANDOM_OCTEON) += octeon-rng.o
 obj-$(CONFIG_HW_RANDOM_NOMADIK) += nomadik-rng.o
 obj-$(CONFIG_HW_RANDOM_PSERIES) += pseries-rng.o
diff --git a/drivers/char/hw_random/imx-rngc.c b/drivers/char/hw_random/imx-rngc.c
new file mode 100644
index 0000000..88db42d
--- /dev/null
+++ b/drivers/char/hw_random/imx-rngc.c
@@ -0,0 +1,331 @@
+/*
+ * RNG driver for Freescale RNGC
+ *
+ * Copyright (C) 2008-2012 Freescale Semiconductor, Inc.
+ * Copyright (C) 2017 Martin Kaiser <martin@kaiser.cx>
+ *
+ * The code contained herein is licensed under the GNU General Public
+ * License. You may obtain a copy of the GNU General Public License
+ * Version 2 or later at the following locations:
+ *
+ * http://www.opensource.org/licenses/gpl-license.html
+ * http://www.gnu.org/copyleft/gpl.html
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/platform_device.h>
+#include <linux/interrupt.h>
+#include <linux/hw_random.h>
+#include <linux/completion.h>
+#include <linux/io.h>
+
+#define RNGC_COMMAND			0x0004
+#define RNGC_CONTROL			0x0008
+#define RNGC_STATUS			0x000C
+#define RNGC_ERROR			0x0010
+#define RNGC_FIFO			0x0014
+
+#define RNGC_CMD_CLR_ERR		0x00000020
+#define RNGC_CMD_CLR_INT		0x00000010
+#define RNGC_CMD_SEED			0x00000002
+#define RNGC_CMD_SELF_TEST		0x00000001
+
+#define RNGC_CTRL_MASK_ERROR		0x00000040
+#define RNGC_CTRL_MASK_DONE		0x00000020
+
+#define RNGC_STATUS_ERROR		0x00010000
+#define RNGC_STATUS_FIFO_LEVEL_MASK	0x00000f00
+#define RNGC_STATUS_FIFO_LEVEL_SHIFT	8
+#define RNGC_STATUS_SEED_DONE		0x00000020
+#define RNGC_STATUS_ST_DONE		0x00000010
+
+#define RNGC_ERROR_STATUS_STAT_ERR	0x00000008
+
+#define RNGC_TIMEOUT  3000 /* 3 sec */
+
+
+static bool self_test = true;
+module_param(self_test, bool, 0);
+
+struct imx_rngc {
+	struct device		*dev;
+	struct clk		*clk;
+	void __iomem		*base;
+	struct hwrng		rng;
+	struct completion	rng_op_done;
+	/*
+	 * err_reg is written only by the irq handler and read only
+	 * when interrupts are masked, we need no spinlock
+	 */
+	u32			err_reg;
+};
+
+
+static inline void imx_rngc_irq_mask_clear(struct imx_rngc *rngc)
+{
+	u32 ctrl, cmd;
+
+	/* mask interrupts */
+	ctrl = readl(rngc->base + RNGC_CONTROL);
+	ctrl |= RNGC_CTRL_MASK_DONE | RNGC_CTRL_MASK_ERROR;
+	writel(ctrl, rngc->base + RNGC_CONTROL);
+
+	/*
+	 * CLR_INT clears the interrupt only if there's no error
+	 * CLR_ERR clear the interrupt and the error register if there
+	 * is an error
+	 */
+	cmd = readl(rngc->base + RNGC_COMMAND);
+	cmd |= RNGC_CMD_CLR_INT | RNGC_CMD_CLR_ERR;
+	writel(cmd, rngc->base + RNGC_COMMAND);
+}
+
+static inline void imx_rngc_irq_unmask(struct imx_rngc *rngc)
+{
+	u32 ctrl;
+
+	ctrl = readl(rngc->base + RNGC_CONTROL);
+	ctrl &= ~(RNGC_CTRL_MASK_DONE | RNGC_CTRL_MASK_ERROR);
+	writel(ctrl, rngc->base + RNGC_CONTROL);
+}
+
+static int imx_rngc_self_test(struct imx_rngc *rngc)
+{
+	u32 cmd;
+	int ret;
+
+	imx_rngc_irq_unmask(rngc);
+
+	/* run self test */
+	cmd = readl(rngc->base + RNGC_COMMAND);
+	writel(cmd | RNGC_CMD_SELF_TEST, rngc->base + RNGC_COMMAND);
+
+	ret = wait_for_completion_timeout(&rngc->rng_op_done, RNGC_TIMEOUT);
+	if (!ret) {
+		imx_rngc_irq_mask_clear(rngc);
+		return -ETIMEDOUT;
+	}
+
+	if (rngc->err_reg != 0)
+		return -EIO;
+
+	return 0;
+}
+
+static int imx_rngc_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct imx_rngc *rngc = container_of(rng, struct imx_rngc, rng);
+	unsigned int status;
+	unsigned int level;
+	int retval = 0;
+
+	while (max >= sizeof(u32)) {
+		status = readl(rngc->base + RNGC_STATUS);
+
+		/* is there some error while reading this random number? */
+		if (status & RNGC_STATUS_ERROR)
+			break;
+
+		/* how many random numbers are in FIFO? [0-16] */
+		level = (status & RNGC_STATUS_FIFO_LEVEL_MASK) >>
+			RNGC_STATUS_FIFO_LEVEL_SHIFT;
+
+		if (level) {
+			/* retrieve a random number from FIFO */
+			*(u32 *)data = readl(rngc->base + RNGC_FIFO);
+
+			retval += sizeof(u32);
+			data += sizeof(u32);
+			max -= sizeof(u32);
+		}
+	}
+
+	return retval ? retval : -EIO;
+}
+
+static irqreturn_t imx_rngc_irq(int irq, void *priv)
+{
+	struct imx_rngc *rngc = (struct imx_rngc *)priv;
+	u32 status;
+
+	/*
+	 * clearing the interrupt will also clear the error register
+	 * read error and status before clearing
+	 */
+	status = readl(rngc->base + RNGC_STATUS);
+	rngc->err_reg = readl(rngc->base + RNGC_ERROR);
+
+	imx_rngc_irq_mask_clear(rngc);
+
+	if (status & (RNGC_STATUS_SEED_DONE | RNGC_STATUS_ST_DONE))
+		complete(&rngc->rng_op_done);
+
+	return IRQ_HANDLED;
+}
+
+static int imx_rngc_init(struct hwrng *rng)
+{
+	struct imx_rngc *rngc = container_of(rng, struct imx_rngc, rng);
+	u32 cmd;
+	int ret;
+
+	/* clear error */
+	cmd = readl(rngc->base + RNGC_COMMAND);
+	writel(cmd | RNGC_CMD_CLR_ERR, rngc->base + RNGC_COMMAND);
+
+	/* create seed, repeat while there is some statistical error */
+	do {
+		imx_rngc_irq_unmask(rngc);
+
+		/* seed creation */
+		cmd = readl(rngc->base + RNGC_COMMAND);
+		writel(cmd | RNGC_CMD_SEED, rngc->base + RNGC_COMMAND);
+
+		ret = wait_for_completion_timeout(&rngc->rng_op_done,
+				RNGC_TIMEOUT);
+
+		if (!ret) {
+			imx_rngc_irq_mask_clear(rngc);
+			return -ETIMEDOUT;
+		}
+
+	} while (rngc->err_reg == RNGC_ERROR_STATUS_STAT_ERR);
+
+	return rngc->err_reg ? -EIO : 0;
+}
+
+static int imx_rngc_probe(struct platform_device *pdev)
+{
+	struct imx_rngc *rngc;
+	struct resource *res;
+	int ret;
+	int irq;
+
+	rngc = devm_kzalloc(&pdev->dev, sizeof(*rngc), GFP_KERNEL);
+	if (!rngc)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	rngc->base = devm_ioremap_resource(&pdev->dev, res);
+	if (IS_ERR(rngc->base))
+		return PTR_ERR(rngc->base);
+
+	rngc->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(rngc->clk)) {
+		dev_err(&pdev->dev, "Can not get rng_clk\n");
+		return PTR_ERR(rngc->clk);
+	}
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq <= 0) {
+		dev_err(&pdev->dev, "Couldn't get irq %d\n", irq);
+		return irq;
+	}
+
+	ret = clk_prepare_enable(rngc->clk);
+	if (ret)
+		return ret;
+
+	ret = devm_request_irq(&pdev->dev,
+			irq, imx_rngc_irq, 0, pdev->name, (void *)rngc);
+	if (ret) {
+		dev_err(rngc->dev, "Can't get interrupt working.\n");
+		goto err;
+	}
+
+	init_completion(&rngc->rng_op_done);
+
+	rngc->rng.name = pdev->name;
+	rngc->rng.init = imx_rngc_init;
+	rngc->rng.read = imx_rngc_read;
+
+	rngc->dev = &pdev->dev;
+	platform_set_drvdata(pdev, rngc);
+
+	imx_rngc_irq_mask_clear(rngc);
+
+	if (self_test) {
+		ret = imx_rngc_self_test(rngc);
+		if (ret) {
+			dev_err(rngc->dev, "FSL RNGC self test failed.\n");
+			goto err;
+		}
+	}
+
+	ret = hwrng_register(&rngc->rng);
+	if (ret) {
+		dev_err(&pdev->dev, "FSL RNGC registering failed (%d)\n", ret);
+		goto err;
+	}
+
+	dev_info(&pdev->dev, "Freescale RNGC registered.\n");
+	return 0;
+
+err:
+	clk_disable_unprepare(rngc->clk);
+
+	return ret;
+}
+
+static int __exit imx_rngc_remove(struct platform_device *pdev)
+{
+	struct imx_rngc *rngc = platform_get_drvdata(pdev);
+
+	hwrng_unregister(&rngc->rng);
+
+	clk_disable_unprepare(rngc->clk);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM
+static int imx_rngc_suspend(struct device *dev)
+{
+	struct imx_rngc *rngc = dev_get_drvdata(dev);
+
+	clk_disable_unprepare(rngc->clk);
+
+	return 0;
+}
+
+static int imx_rngc_resume(struct device *dev)
+{
+	struct imx_rngc *rngc = dev_get_drvdata(dev);
+
+	clk_prepare_enable(rngc->clk);
+
+	return 0;
+}
+
+static const struct dev_pm_ops imx_rngc_pm_ops = {
+	.suspend	= imx_rngc_suspend,
+	.resume		= imx_rngc_resume,
+};
+#endif
+
+static const struct of_device_id imx_rngc_dt_ids[] = {
+	{ .compatible = "fsl,imx25-rngb", .data = NULL, },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, imx_rngc_dt_ids);
+
+static struct platform_driver imx_rngc_driver = {
+	.driver = {
+		.name = "imx_rngc",
+#ifdef CONFIG_PM
+		.pm = &imx_rngc_pm_ops,
+#endif
+		.of_match_table = imx_rngc_dt_ids,
+	},
+	.remove = __exit_p(imx_rngc_remove),
+};
+
+module_platform_driver_probe(imx_rngc_driver, imx_rngc_probe);
+
+MODULE_AUTHOR("Freescale Semiconductor, Inc.");
+MODULE_DESCRIPTION("H/W RNGC driver for i.MX");
+MODULE_LICENSE("GPL");
-- 
2.1.4