nvmem: imx-ocotp: add write support

Implement write routine for OCOTP controller found in i.MX6 SoC's.
Furthermore add locking to the read function to prevent race conditions.
The write routine code is based on the fsl_otp driver from Freescale.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/nvmem/imx-ocotp.txt

@@ -14,10 +14,14 @@ Required properties:
 - reg: Should contain the register base and length.
 - clocks: Should contain a phandle pointing to the gated peripheral clock.
 
+Optional properties:
+- read-only: disable write access
+
 Example:
 
 	ocotp: ocotp@021bc000 {
 		compatible = "fsl,imx6q-ocotp", "syscon";
 		reg = <0x021bc000 0x4000>;
 		clocks = <&clks IMX6QDL_CLK_IIM>;
+		read-only;
 	};

drivers/nvmem/imx-ocotp.c

@@ -7,6 +7,9 @@
  * Copyright (c) 2010 Baruch Siach <baruch@tkos.co.il>,
  *	Orex Computed Radiography
  *
+ * Write support based on the fsl_otp driver,
+ * Copyright (C) 2010-2013 Freescale Semiconductor, Inc
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2
  * as published by the Free Software Foundation.
@@ -24,6 +27,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
+#include <linux/delay.h>
 
 #define IMX_OCOTP_OFFSET_B0W0		0x400 /* Offset from base address of the
 					       * OTP Bank0 Word0
@@ -31,20 +35,69 @@
 #define IMX_OCOTP_OFFSET_PER_WORD	0x10  /* Offset between the start addr
 					       * of two consecutive OTP words.
 					       */
+
 #define IMX_OCOTP_ADDR_CTRL		0x0000
+#define IMX_OCOTP_ADDR_CTRL_SET		0x0004
 #define IMX_OCOTP_ADDR_CTRL_CLR		0x0008
+#define IMX_OCOTP_ADDR_TIMING		0x0010
+#define IMX_OCOTP_ADDR_DATA		0x0020
 
+#define IMX_OCOTP_BM_CTRL_ADDR		0x0000007F
+#define IMX_OCOTP_BM_CTRL_BUSY		0x00000100
 #define IMX_OCOTP_BM_CTRL_ERROR		0x00000200
+#define IMX_OCOTP_BM_CTRL_REL_SHADOWS	0x00000400
 
+#define DEF_RELAX			20 /* > 16.5ns */
+#define IMX_OCOTP_WR_UNLOCK		0x3E770000
 #define IMX_OCOTP_READ_LOCKED_VAL	0xBADABADA
 
+static DEFINE_MUTEX(ocotp_mutex);
+
 struct ocotp_priv {
 	struct device *dev;
 	struct clk *clk;
 	void __iomem *base;
 	unsigned int nregs;
+	struct nvmem_config *config;
 };
 
+static int imx_ocotp_wait_for_busy(void __iomem *base, u32 flags)
+{
+	int count;
+	u32 c, mask;
+
+	mask = IMX_OCOTP_BM_CTRL_BUSY | IMX_OCOTP_BM_CTRL_ERROR | flags;
+
+	for (count = 10000; count >= 0; count--) {
+		c = readl(base + IMX_OCOTP_ADDR_CTRL);
+		if (!(c & mask))
+			break;
+		cpu_relax();
+	}
+
+	if (count < 0) {
+		/* HW_OCOTP_CTRL[ERROR] will be set under the following
+		 * conditions:
+		 * - A write is performed to a shadow register during a shadow
+		 *   reload (essentially, while HW_OCOTP_CTRL[RELOAD_SHADOWS] is
+		 *   set. In addition, the contents of the shadow register shall
+		 *   not be updated.
+		 * - A write is performed to a shadow register which has been
+		 *   locked.
+		 * - A read is performed to from a shadow register which has
+		 *   been read locked.
+		 * - A program is performed to a fuse word which has been locked
+		 * - A read is performed to from a fuse word which has been read
+		 *   locked.
+		 */
+		if (c & IMX_OCOTP_BM_CTRL_ERROR)
+			return -EPERM;
+		return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
 static void imx_ocotp_clr_err_if_set(void __iomem *base)
 {
 	u32 c;
@@ -71,12 +124,21 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 	if (count > (priv->nregs - index))
 		count = priv->nregs - index;
 
+	mutex_lock(&ocotp_mutex);
+
 	ret = clk_prepare_enable(priv->clk);
 	if (ret < 0) {
+		mutex_unlock(&ocotp_mutex);
 		dev_err(priv->dev, "failed to prepare/enable ocotp clk\n");
 		return ret;
 	}
 
+	ret = imx_ocotp_wait_for_busy(priv->base, 0);
+	if (ret < 0) {
+		dev_err(priv->dev, "timeout during read setup\n");
+		goto read_end;
+	}
+
 	for (i = index; i < (index + count); i++) {
 		*buf++ = readl(priv->base + IMX_OCOTP_OFFSET_B0W0 +
 			       i * IMX_OCOTP_OFFSET_PER_WORD);
@@ -90,18 +152,160 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 		if (*(buf - 1) == IMX_OCOTP_READ_LOCKED_VAL)
 			imx_ocotp_clr_err_if_set(priv->base);
 	}
+	ret = 0;
 
+read_end:
 	clk_disable_unprepare(priv->clk);
-	return 0;
+	mutex_unlock(&ocotp_mutex);
+	return ret;
+}
+
+static int imx_ocotp_write(void *context, unsigned int offset, void *val,
+			   size_t bytes)
+{
+	struct ocotp_priv *priv = context;
+	u32 *buf = val;
+	int ret;
+
+	unsigned long clk_rate = 0;
+	unsigned long strobe_read, relax, strobe_prog;
+	u32 timing = 0;
+	u32 ctrl;
+	u8 waddr;
+
+	/* allow only writing one complete OTP word at a time */
+	if ((bytes != priv->config->word_size) ||
+	    (offset % priv->config->word_size))
+		return -EINVAL;
+
+	mutex_lock(&ocotp_mutex);
+
+	ret = clk_prepare_enable(priv->clk);
+	if (ret < 0) {
+		mutex_unlock(&ocotp_mutex);
+		dev_err(priv->dev, "failed to prepare/enable ocotp clk\n");
+		return ret;
+	}
+
+	/* 47.3.1.3.1
+	 * Program HW_OCOTP_TIMING[STROBE_PROG] and HW_OCOTP_TIMING[RELAX]
+	 * fields with timing values to match the current frequency of the
+	 * ipg_clk. OTP writes will work at maximum bus frequencies as long
+	 * as the HW_OCOTP_TIMING parameters are set correctly.
+	 */
+	clk_rate = clk_get_rate(priv->clk);
+
+	relax = clk_rate / (1000000000 / DEF_RELAX) - 1;
+	strobe_prog = clk_rate / (1000000000 / 10000) + 2 * (DEF_RELAX + 1) - 1;
+	strobe_read = clk_rate / (1000000000 / 40) + 2 * (DEF_RELAX + 1) - 1;
+
+	timing = strobe_prog & 0x00000FFF;
+	timing |= (relax       << 12) & 0x0000F000;
+	timing |= (strobe_read << 16) & 0x003F0000;
+
+	writel(timing, priv->base + IMX_OCOTP_ADDR_TIMING);
+
+	/* 47.3.1.3.2
+	 * Check that HW_OCOTP_CTRL[BUSY] and HW_OCOTP_CTRL[ERROR] are clear.
+	 * Overlapped accesses are not supported by the controller. Any pending
+	 * write or reload must be completed before a write access can be
+	 * requested.
+	 */
+	ret = imx_ocotp_wait_for_busy(priv->base, 0);
+	if (ret < 0) {
+		dev_err(priv->dev, "timeout during timing setup\n");
+		goto write_end;
+	}
+
+	/* 47.3.1.3.3
+	 * Write the requested address to HW_OCOTP_CTRL[ADDR] and program the
+	 * unlock code into HW_OCOTP_CTRL[WR_UNLOCK]. This must be programmed
+	 * for each write access. The lock code is documented in the register
+	 * description. Both the unlock code and address can be written in the
+	 * same operation.
+	 */
+	/* OTP write/read address specifies one of 128 word address locations */
+	waddr = offset / 4;
+
+	ctrl = readl(priv->base + IMX_OCOTP_ADDR_CTRL);
+	ctrl &= ~IMX_OCOTP_BM_CTRL_ADDR;
+	ctrl |= waddr & IMX_OCOTP_BM_CTRL_ADDR;
+	ctrl |= IMX_OCOTP_WR_UNLOCK;
+
+	writel(ctrl, priv->base + IMX_OCOTP_ADDR_CTRL);
+
+	/* 47.3.1.3.4
+	 * Write the data to the HW_OCOTP_DATA register. This will automatically
+	 * set HW_OCOTP_CTRL[BUSY] and clear HW_OCOTP_CTRL[WR_UNLOCK]. To
+	 * protect programming same OTP bit twice, before program OCOTP will
+	 * automatically read fuse value in OTP and use read value to mask
+	 * program data. The controller will use masked program data to program
+	 * a 32-bit word in the OTP per the address in HW_OCOTP_CTRL[ADDR]. Bit
+	 * fields with 1's will result in that OTP bit being programmed. Bit
+	 * fields with 0's will be ignored. At the same time that the write is
+	 * accepted, the controller makes an internal copy of
+	 * HW_OCOTP_CTRL[ADDR] which cannot be updated until the next write
+	 * sequence is initiated. This copy guarantees that erroneous writes to
+	 * HW_OCOTP_CTRL[ADDR] will not affect an active write operation. It
+	 * should also be noted that during the programming HW_OCOTP_DATA will
+	 * shift right (with zero fill). This shifting is required to program
+	 * the OTP serially. During the write operation, HW_OCOTP_DATA cannot be
+	 * modified.
+	 */
+	writel(*buf, priv->base + IMX_OCOTP_ADDR_DATA);
+
+	/* 47.4.1.4.5
+	 * Once complete, the controller will clear BUSY. A write request to a
+	 * protected or locked region will result in no OTP access and no
+	 * setting of HW_OCOTP_CTRL[BUSY]. In addition HW_OCOTP_CTRL[ERROR] will
+	 * be set. It must be cleared by software before any new write access
+	 * can be issued.
+	 */
+	ret = imx_ocotp_wait_for_busy(priv->base, 0);
+	if (ret < 0) {
+		if (ret == -EPERM) {
+			dev_err(priv->dev, "failed write to locked region");
+			imx_ocotp_clr_err_if_set(priv->base);
+		} else {
+			dev_err(priv->dev, "timeout during data write\n");
+		}
+		goto write_end;
+	}
+
+	/* 47.3.1.4
+	 * Write Postamble: Due to internal electrical characteristics of the
+	 * OTP during writes, all OTP operations following a write must be
+	 * separated by 2 us after the clearing of HW_OCOTP_CTRL_BUSY following
+	 * the write.
+	 */
+	udelay(2);
+
+	/* reload all shadow registers */
+	writel(IMX_OCOTP_BM_CTRL_REL_SHADOWS,
+	       priv->base + IMX_OCOTP_ADDR_CTRL_SET);
+	ret = imx_ocotp_wait_for_busy(priv->base,
+				      IMX_OCOTP_BM_CTRL_REL_SHADOWS);
+	if (ret < 0) {
+		dev_err(priv->dev, "timeout during shadow register reload\n");
+		goto write_end;
+	}
+
+write_end:
+	clk_disable_unprepare(priv->clk);
+	mutex_unlock(&ocotp_mutex);
+	if (ret < 0)
+		return ret;
+	return bytes;
 }
 
 static struct nvmem_config imx_ocotp_nvmem_config = {
 	.name = "imx-ocotp",
-	.read_only = true,
+	.read_only = false,
 	.word_size = 4,
 	.stride = 4,
 	.owner = THIS_MODULE,
 	.reg_read = imx_ocotp_read,
+	.reg_write = imx_ocotp_write,
 };
 
 static const struct of_device_id imx_ocotp_dt_ids[] = {
@@ -142,7 +346,9 @@ static int imx_ocotp_probe(struct platform_device *pdev)
 	imx_ocotp_nvmem_config.size = 4 * priv->nregs;
 	imx_ocotp_nvmem_config.dev = dev;
 	imx_ocotp_nvmem_config.priv = priv;
+	priv->config = &imx_ocotp_nvmem_config;
 	nvmem = nvmem_register(&imx_ocotp_nvmem_config);
+
 	if (IS_ERR(nvmem))
 		return PTR_ERR(nvmem);