[PATCH 2/2] nvmem: imx-ocotp: add write support

[Richard Leitner <richard.leitner-WcANXNA0UjBBDgjK7y7TUQ@public.gmane.org>]

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-WcANXNA0UjBBDgjK7y7TUQ@public.gmane.org>
---
 .../devicetree/bindings/nvmem/imx-ocotp.txt        |   4 +
 drivers/nvmem/imx-ocotp.c                          | 210 ++++++++++++++++++++-
 2 files changed, 212 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
index 966a72e..4b04356 100644
--- a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
+++ b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
@@ -13,10 +13,14 @@ 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;
 	};
diff --git a/drivers/nvmem/imx-ocotp.c b/drivers/nvmem/imx-ocotp.c
index e2b62b3..eb55b41 100644
--- a/drivers/nvmem/imx-ocotp.c
+++ b/drivers/nvmem/imx-ocotp.c
@@ -7,6 +7,9 @@
  * Copyright (c) 2010 Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>,
  *	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[] = {
@@ -139,7 +343,9 @@ 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);
 
-- 
2.1.4

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