diff mbox series

[v4,02/14] riscv: sifive: fu540: Use OTP DM driver for serial environment variable

Message ID 20200224083247.29086-3-pragnesh.patel@sifive.com
State New
Headers show
Series RISC-V SiFive FU540 support SPL | expand

Commit Message

Pragnesh Patel Feb. 24, 2020, 8:32 a.m. UTC
Use the OTP DM driver to set the serial environment variable.

Signed-off-by: Pragnesh Patel <pragnesh.patel at sifive.com>
---
 arch/riscv/dts/fu540-c000-u-boot.dtsi         |  14 +++
 .../dts/hifive-unleashed-a00-u-boot.dtsi      |   6 +
 board/sifive/fu540/Kconfig                    |   2 +
 board/sifive/fu540/fu540.c                    | 113 +++++++-----------
 4 files changed, 62 insertions(+), 73 deletions(-)
 create mode 100644 arch/riscv/dts/fu540-c000-u-boot.dtsi
 create mode 100644 arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi

Comments

Patrick Delaunay Feb. 24, 2020, 6 p.m. UTC | #1
Hi,

Just a warning as I had the same issue with 8729b1ae2cbd ("misc: Update read() and write()  methods to return bytes xfered")

> From: U-Boot <u-boot-bounces at lists.denx.de> On Behalf Of Pragnesh Patel
> Sent: lundi 24 f?vrier 2020 09:33
> 
> Use the OTP DM driver to set the serial environment variable.
> 
> Signed-off-by: Pragnesh Patel <pragnesh.patel at sifive.com>
> ---
>  arch/riscv/dts/fu540-c000-u-boot.dtsi         |  14 +++
>  .../dts/hifive-unleashed-a00-u-boot.dtsi      |   6 +
>  board/sifive/fu540/Kconfig                    |   2 +
>  board/sifive/fu540/fu540.c                    | 113 +++++++-----------
>  4 files changed, 62 insertions(+), 73 deletions(-)  create mode 100644
> arch/riscv/dts/fu540-c000-u-boot.dtsi
>  create mode 100644 arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
> 
> diff --git a/arch/riscv/dts/fu540-c000-u-boot.dtsi b/arch/riscv/dts/fu540-c000-u-
> boot.dtsi
> new file mode 100644
> index 0000000000..31fd113c7d
> --- /dev/null
> +++ b/arch/riscv/dts/fu540-c000-u-boot.dtsi
> @@ -0,0 +1,14 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * (C) Copyright 2019 SiFive, Inc
> + */
> +
> +/ {
> +	soc {
> +		otp: otp at 10070000 {
> +			compatible = "sifive,fu540-otp";
> +			reg = <0x0 0x10070000 0x0 0x0FFF>;
> +			fuse-count = <0x1000>;
> +		};
> +	};
> +};
> diff --git a/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi b/arch/riscv/dts/hifive-
> unleashed-a00-u-boot.dtsi
> new file mode 100644
> index 0000000000..bec0d19134
> --- /dev/null
> +++ b/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
> @@ -0,0 +1,6 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 SiFive, Inc
> + */
> +
> +#include "fu540-c000-u-boot.dtsi"
> diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig index
> 5ca21474de..900197bbb2 100644
> --- a/board/sifive/fu540/Kconfig
> +++ b/board/sifive/fu540/Kconfig
> @@ -48,5 +48,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
>  	imply SIFIVE_GPIO
>  	imply CMD_GPIO
>  	imply SMP
> +	imply MISC
> +	imply SIFIVE_OTP
> 
>  endif
> diff --git a/board/sifive/fu540/fu540.c b/board/sifive/fu540/fu540.c index
> 47a2090251..409471effc 100644
> --- a/board/sifive/fu540/fu540.c
> +++ b/board/sifive/fu540/fu540.c
> @@ -10,94 +10,61 @@
>  #include <dm.h>
>  #include <linux/delay.h>
>  #include <linux/io.h>
> +#include <misc.h>
> 
> -#ifdef CONFIG_MISC_INIT_R
> -
> -#define FU540_OTP_BASE_ADDR			0x10070000
> -
> -struct fu540_otp_regs {
> -	u32 pa;     /* Address input */
> -	u32 paio;   /* Program address input */
> -	u32 pas;    /* Program redundancy cell selection input */
> -	u32 pce;    /* OTP Macro enable input */
> -	u32 pclk;   /* Clock input */
> -	u32 pdin;   /* Write data input */
> -	u32 pdout;  /* Read data output */
> -	u32 pdstb;  /* Deep standby mode enable input (active low) */
> -	u32 pprog;  /* Program mode enable input */
> -	u32 ptc;    /* Test column enable input */
> -	u32 ptm;    /* Test mode enable input */
> -	u32 ptm_rep;/* Repair function test mode enable input */
> -	u32 ptr;    /* Test row enable input */
> -	u32 ptrim;  /* Repair function enable input */
> -	u32 pwe;    /* Write enable input (defines program cycle) */
> -} __packed;
> -
> -#define BYTES_PER_FUSE				4
> -#define NUM_FUSES				0x1000
> -
> -static int fu540_otp_read(int offset, void *buf, int size) -{
> -	struct fu540_otp_regs *regs = (void __iomem
> *)FU540_OTP_BASE_ADDR;
> -	unsigned int i;
> -	int fuseidx = offset / BYTES_PER_FUSE;
> -	int fusecount = size / BYTES_PER_FUSE;
> -	u32 fusebuf[fusecount];
> -
> -	/* check bounds */
> -	if (offset < 0 || size < 0)
> -		return -EINVAL;
> -	if (fuseidx >= NUM_FUSES)
> -		return -EINVAL;
> -	if ((fuseidx + fusecount) > NUM_FUSES)
> -		return -EINVAL;
> -
> -	/* init OTP */
> -	writel(0x01, &regs->pdstb); /* wake up from stand-by */
> -	writel(0x01, &regs->ptrim); /* enable repair function */
> -	writel(0x01, &regs->pce);   /* enable input */
> -
> -	/* read all requested fuses */
> -	for (i = 0; i < fusecount; i++, fuseidx++) {
> -		writel(fuseidx, &regs->pa);
> -
> -		/* cycle clock to read */
> -		writel(0x01, &regs->pclk);
> -		mdelay(1);
> -		writel(0x00, &regs->pclk);
> -		mdelay(1);
> -
> -		/* read the value */
> -		fusebuf[i] = readl(&regs->pdout);
> -	}
> -
> -	/* shut down */
> -	writel(0, &regs->pce);
> -	writel(0, &regs->ptrim);
> -	writel(0, &regs->pdstb);
> -
> -	/* copy out */
> -	memcpy(buf, fusebuf, size);
> +/*
> + * This define is a value used for error/unknown serial.
> + * If we really care about distinguishing errors and 0 is
> + * valid, we'll need a different one.
> + */
> +#define ERROR_READING_SERIAL_NUMBER       0
> 
> -	return 0;
> -}
> +#ifdef CONFIG_MISC_INIT_R
> 
> -static u32 fu540_read_serialnum(void)
> +#if CONFIG_IS_ENABLED(SIFIVE_OTP)
> +static u32 otp_read_serialnum(struct udevice *dev)
>  {
>  	int ret;
>  	u32 serial[2] = {0};
> 
>  	for (int i = 0xfe * 4; i > 0; i -= 8) {
> -		ret = fu540_otp_read(i, serial, sizeof(serial));
> +		ret = misc_read(dev, i, serial, sizeof(serial));
> +
>  		if (ret) {

Warning here, misc_read returns now the size of the data (sizeof(serial)), 
since commit 8729b1ae2cbd ("misc: Update read() and write() methods to return bytes xfered")

So I think the test need to change to

if (ret < 0)

or 

if (ret != sizeof(serial))

> -			printf("%s: error reading from OTP\n", __func__);
> +			printf("%s: error reading serial from OTP\n", __func__);
>  			break;
>  		}
> +
>  		if (serial[0] == ~serial[1])
>  			return serial[0];
>  	}
> 
> -	return 0;
> +	return ERROR_READING_SERIAL_NUMBER;
> +}
> +#endif
> +
> +static u32 fu540_read_serialnum(void)
> +{
> +	u32 serial = ERROR_READING_SERIAL_NUMBER;
> +
> +#if CONFIG_IS_ENABLED(SIFIVE_OTP)
> +	struct udevice *dev;
> +	int ret;
> +
> +	// init OTP
> +	ret = uclass_get_device_by_driver(UCLASS_MISC,
> +					  DM_GET_DRIVER(sifive_otp), &dev);
> +
> +	if (ret) {
> +		debug("%s: could not find otp device\n", __func__);
> +		return serial;
> +	}
> +
> +	// read serial from OTP and set env var
> +	serial = otp_read_serialnum(dev);
> +#endif
> +
> +	return serial;
>  }
> 
>  static void fu540_setup_macaddr(u32 serialnum)
> --
> 2.17.1

Patrick
Pragnesh Patel Feb. 25, 2020, 11:38 a.m. UTC | #2
Hi Patrick,

>-----Original Message-----
>From: Patrick DELAUNAY <patrick.delaunay at st.com>
>Sent: 24 February 2020 23:30
>To: Pragnesh Patel <pragnesh.patel at sifive.com>; u-boot at lists.denx.de
>Cc: atish.patra at wdc.com; palmerdabbelt at google.com;
>bmeng.cn at gmail.com; Paul Walmsley ( Sifive) <paul.walmsley at sifive.com>;
>jagan at amarulasolutions.com; Troy Benjegerdes ( Sifive)
><troy.benjegerdes at sifive.com>; anup.patel at wdc.com; Sagar Kadam
><sagar.kadam at sifive.com>; Rick Chen <rick at andestech.com>
>Subject: RE: [PATCH v4 02/14] riscv: sifive: fu540: Use OTP DM driver for serial
>environment variable
>
>Hi,
>
>Just a warning as I had the same issue with 8729b1ae2cbd ("misc: Update
>read() and write()  methods to return bytes xfered")
>
>> From: U-Boot <u-boot-bounces at lists.denx.de> On Behalf Of Pragnesh
>> Patel
>> Sent: lundi 24 f?vrier 2020 09:33
>>
>> Use the OTP DM driver to set the serial environment variable.
>>
>> Signed-off-by: Pragnesh Patel <pragnesh.patel at sifive.com>
>> ---
>>  arch/riscv/dts/fu540-c000-u-boot.dtsi         |  14 +++
>>  .../dts/hifive-unleashed-a00-u-boot.dtsi      |   6 +
>>  board/sifive/fu540/Kconfig                    |   2 +
>>  board/sifive/fu540/fu540.c                    | 113 +++++++-----------
>>  4 files changed, 62 insertions(+), 73 deletions(-)  create mode
>> 100644 arch/riscv/dts/fu540-c000-u-boot.dtsi
>>  create mode 100644 arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
>>
>> diff --git a/arch/riscv/dts/fu540-c000-u-boot.dtsi
>> b/arch/riscv/dts/fu540-c000-u- boot.dtsi new file mode 100644 index
>> 0000000000..31fd113c7d
>> --- /dev/null
>> +++ b/arch/riscv/dts/fu540-c000-u-boot.dtsi
>> @@ -0,0 +1,14 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * (C) Copyright 2019 SiFive, Inc
>> + */
>> +
>> +/ {
>> +	soc {
>> +		otp: otp at 10070000 {
>> +			compatible = "sifive,fu540-otp";
>> +			reg = <0x0 0x10070000 0x0 0x0FFF>;
>> +			fuse-count = <0x1000>;
>> +		};
>> +	};
>> +};
>> diff --git a/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
>> b/arch/riscv/dts/hifive- unleashed-a00-u-boot.dtsi new file mode
>> 100644 index 0000000000..bec0d19134
>> --- /dev/null
>> +++ b/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
>> @@ -0,0 +1,6 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Copyright (C) 2019 SiFive, Inc
>> + */
>> +
>> +#include "fu540-c000-u-boot.dtsi"
>> diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig
>> index
>> 5ca21474de..900197bbb2 100644
>> --- a/board/sifive/fu540/Kconfig
>> +++ b/board/sifive/fu540/Kconfig
>> @@ -48,5 +48,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
>>  	imply SIFIVE_GPIO
>>  	imply CMD_GPIO
>>  	imply SMP
>> +	imply MISC
>> +	imply SIFIVE_OTP
>>
>>  endif
>> diff --git a/board/sifive/fu540/fu540.c b/board/sifive/fu540/fu540.c
>> index 47a2090251..409471effc 100644
>> --- a/board/sifive/fu540/fu540.c
>> +++ b/board/sifive/fu540/fu540.c
>> @@ -10,94 +10,61 @@
>>  #include <dm.h>
>>  #include <linux/delay.h>
>>  #include <linux/io.h>
>> +#include <misc.h>
>>
>> -#ifdef CONFIG_MISC_INIT_R
>> -
>> -#define FU540_OTP_BASE_ADDR			0x10070000
>> -
>> -struct fu540_otp_regs {
>> -	u32 pa;     /* Address input */
>> -	u32 paio;   /* Program address input */
>> -	u32 pas;    /* Program redundancy cell selection input */
>> -	u32 pce;    /* OTP Macro enable input */
>> -	u32 pclk;   /* Clock input */
>> -	u32 pdin;   /* Write data input */
>> -	u32 pdout;  /* Read data output */
>> -	u32 pdstb;  /* Deep standby mode enable input (active low) */
>> -	u32 pprog;  /* Program mode enable input */
>> -	u32 ptc;    /* Test column enable input */
>> -	u32 ptm;    /* Test mode enable input */
>> -	u32 ptm_rep;/* Repair function test mode enable input */
>> -	u32 ptr;    /* Test row enable input */
>> -	u32 ptrim;  /* Repair function enable input */
>> -	u32 pwe;    /* Write enable input (defines program cycle) */
>> -} __packed;
>> -
>> -#define BYTES_PER_FUSE				4
>> -#define NUM_FUSES				0x1000
>> -
>> -static int fu540_otp_read(int offset, void *buf, int size) -{
>> -	struct fu540_otp_regs *regs = (void __iomem
>> *)FU540_OTP_BASE_ADDR;
>> -	unsigned int i;
>> -	int fuseidx = offset / BYTES_PER_FUSE;
>> -	int fusecount = size / BYTES_PER_FUSE;
>> -	u32 fusebuf[fusecount];
>> -
>> -	/* check bounds */
>> -	if (offset < 0 || size < 0)
>> -		return -EINVAL;
>> -	if (fuseidx >= NUM_FUSES)
>> -		return -EINVAL;
>> -	if ((fuseidx + fusecount) > NUM_FUSES)
>> -		return -EINVAL;
>> -
>> -	/* init OTP */
>> -	writel(0x01, &regs->pdstb); /* wake up from stand-by */
>> -	writel(0x01, &regs->ptrim); /* enable repair function */
>> -	writel(0x01, &regs->pce);   /* enable input */
>> -
>> -	/* read all requested fuses */
>> -	for (i = 0; i < fusecount; i++, fuseidx++) {
>> -		writel(fuseidx, &regs->pa);
>> -
>> -		/* cycle clock to read */
>> -		writel(0x01, &regs->pclk);
>> -		mdelay(1);
>> -		writel(0x00, &regs->pclk);
>> -		mdelay(1);
>> -
>> -		/* read the value */
>> -		fusebuf[i] = readl(&regs->pdout);
>> -	}
>> -
>> -	/* shut down */
>> -	writel(0, &regs->pce);
>> -	writel(0, &regs->ptrim);
>> -	writel(0, &regs->pdstb);
>> -
>> -	/* copy out */
>> -	memcpy(buf, fusebuf, size);
>> +/*
>> + * This define is a value used for error/unknown serial.
>> + * If we really care about distinguishing errors and 0 is
>> + * valid, we'll need a different one.
>> + */
>> +#define ERROR_READING_SERIAL_NUMBER       0
>>
>> -	return 0;
>> -}
>> +#ifdef CONFIG_MISC_INIT_R
>>
>> -static u32 fu540_read_serialnum(void)
>> +#if CONFIG_IS_ENABLED(SIFIVE_OTP)
>> +static u32 otp_read_serialnum(struct udevice *dev)
>>  {
>>  	int ret;
>>  	u32 serial[2] = {0};
>>
>>  	for (int i = 0xfe * 4; i > 0; i -= 8) {
>> -		ret = fu540_otp_read(i, serial, sizeof(serial));
>> +		ret = misc_read(dev, i, serial, sizeof(serial));
>> +
>>  		if (ret) {
>
>Warning here, misc_read returns now the size of the data (sizeof(serial)),
>since commit 8729b1ae2cbd ("misc: Update read() and write() methods to
>return bytes xfered")
>
>So I think the test need to change to
>
>if (ret < 0)
>
>or
>
>if (ret != sizeof(serial))
>

Yes, you are right. Will update in v5. Thanks for the review.

>> -			printf("%s: error reading from OTP\n", __func__);
>> +			printf("%s: error reading serial from OTP\n",
>__func__);
>>  			break;
>>  		}
>> +
>>  		if (serial[0] == ~serial[1])
>>  			return serial[0];
>>  	}
>>
>> -	return 0;
>> +	return ERROR_READING_SERIAL_NUMBER;
>> +}
>> +#endif
>> +
>> +static u32 fu540_read_serialnum(void) {
>> +	u32 serial = ERROR_READING_SERIAL_NUMBER;
>> +
>> +#if CONFIG_IS_ENABLED(SIFIVE_OTP)
>> +	struct udevice *dev;
>> +	int ret;
>> +
>> +	// init OTP
>> +	ret = uclass_get_device_by_driver(UCLASS_MISC,
>> +					  DM_GET_DRIVER(sifive_otp), &dev);
>> +
>> +	if (ret) {
>> +		debug("%s: could not find otp device\n", __func__);
>> +		return serial;
>> +	}
>> +
>> +	// read serial from OTP and set env var
>> +	serial = otp_read_serialnum(dev);
>> +#endif
>> +
>> +	return serial;
>>  }
>>
>>  static void fu540_setup_macaddr(u32 serialnum)
>> --
>> 2.17.1
>
>Patrick
diff mbox series

Patch

diff --git a/arch/riscv/dts/fu540-c000-u-boot.dtsi b/arch/riscv/dts/fu540-c000-u-boot.dtsi
new file mode 100644
index 0000000000..31fd113c7d
--- /dev/null
+++ b/arch/riscv/dts/fu540-c000-u-boot.dtsi
@@ -0,0 +1,14 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * (C) Copyright 2019 SiFive, Inc
+ */
+
+/ {
+	soc {
+		otp: otp at 10070000 {
+			compatible = "sifive,fu540-otp";
+			reg = <0x0 0x10070000 0x0 0x0FFF>;
+			fuse-count = <0x1000>;
+		};
+	};
+};
diff --git a/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi b/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
new file mode 100644
index 0000000000..bec0d19134
--- /dev/null
+++ b/arch/riscv/dts/hifive-unleashed-a00-u-boot.dtsi
@@ -0,0 +1,6 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 SiFive, Inc
+ */
+
+#include "fu540-c000-u-boot.dtsi"
diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig
index 5ca21474de..900197bbb2 100644
--- a/board/sifive/fu540/Kconfig
+++ b/board/sifive/fu540/Kconfig
@@ -48,5 +48,7 @@  config BOARD_SPECIFIC_OPTIONS # dummy
 	imply SIFIVE_GPIO
 	imply CMD_GPIO
 	imply SMP
+	imply MISC
+	imply SIFIVE_OTP
 
 endif
diff --git a/board/sifive/fu540/fu540.c b/board/sifive/fu540/fu540.c
index 47a2090251..409471effc 100644
--- a/board/sifive/fu540/fu540.c
+++ b/board/sifive/fu540/fu540.c
@@ -10,94 +10,61 @@ 
 #include <dm.h>
 #include <linux/delay.h>
 #include <linux/io.h>
+#include <misc.h>
 
-#ifdef CONFIG_MISC_INIT_R
-
-#define FU540_OTP_BASE_ADDR			0x10070000
-
-struct fu540_otp_regs {
-	u32 pa;     /* Address input */
-	u32 paio;   /* Program address input */
-	u32 pas;    /* Program redundancy cell selection input */
-	u32 pce;    /* OTP Macro enable input */
-	u32 pclk;   /* Clock input */
-	u32 pdin;   /* Write data input */
-	u32 pdout;  /* Read data output */
-	u32 pdstb;  /* Deep standby mode enable input (active low) */
-	u32 pprog;  /* Program mode enable input */
-	u32 ptc;    /* Test column enable input */
-	u32 ptm;    /* Test mode enable input */
-	u32 ptm_rep;/* Repair function test mode enable input */
-	u32 ptr;    /* Test row enable input */
-	u32 ptrim;  /* Repair function enable input */
-	u32 pwe;    /* Write enable input (defines program cycle) */
-} __packed;
-
-#define BYTES_PER_FUSE				4
-#define NUM_FUSES				0x1000
-
-static int fu540_otp_read(int offset, void *buf, int size)
-{
-	struct fu540_otp_regs *regs = (void __iomem *)FU540_OTP_BASE_ADDR;
-	unsigned int i;
-	int fuseidx = offset / BYTES_PER_FUSE;
-	int fusecount = size / BYTES_PER_FUSE;
-	u32 fusebuf[fusecount];
-
-	/* check bounds */
-	if (offset < 0 || size < 0)
-		return -EINVAL;
-	if (fuseidx >= NUM_FUSES)
-		return -EINVAL;
-	if ((fuseidx + fusecount) > NUM_FUSES)
-		return -EINVAL;
-
-	/* init OTP */
-	writel(0x01, &regs->pdstb); /* wake up from stand-by */
-	writel(0x01, &regs->ptrim); /* enable repair function */
-	writel(0x01, &regs->pce);   /* enable input */
-
-	/* read all requested fuses */
-	for (i = 0; i < fusecount; i++, fuseidx++) {
-		writel(fuseidx, &regs->pa);
-
-		/* cycle clock to read */
-		writel(0x01, &regs->pclk);
-		mdelay(1);
-		writel(0x00, &regs->pclk);
-		mdelay(1);
-
-		/* read the value */
-		fusebuf[i] = readl(&regs->pdout);
-	}
-
-	/* shut down */
-	writel(0, &regs->pce);
-	writel(0, &regs->ptrim);
-	writel(0, &regs->pdstb);
-
-	/* copy out */
-	memcpy(buf, fusebuf, size);
+/*
+ * This define is a value used for error/unknown serial.
+ * If we really care about distinguishing errors and 0 is
+ * valid, we'll need a different one.
+ */
+#define ERROR_READING_SERIAL_NUMBER       0
 
-	return 0;
-}
+#ifdef CONFIG_MISC_INIT_R
 
-static u32 fu540_read_serialnum(void)
+#if CONFIG_IS_ENABLED(SIFIVE_OTP)
+static u32 otp_read_serialnum(struct udevice *dev)
 {
 	int ret;
 	u32 serial[2] = {0};
 
 	for (int i = 0xfe * 4; i > 0; i -= 8) {
-		ret = fu540_otp_read(i, serial, sizeof(serial));
+		ret = misc_read(dev, i, serial, sizeof(serial));
+
 		if (ret) {
-			printf("%s: error reading from OTP\n", __func__);
+			printf("%s: error reading serial from OTP\n", __func__);
 			break;
 		}
+
 		if (serial[0] == ~serial[1])
 			return serial[0];
 	}
 
-	return 0;
+	return ERROR_READING_SERIAL_NUMBER;
+}
+#endif
+
+static u32 fu540_read_serialnum(void)
+{
+	u32 serial = ERROR_READING_SERIAL_NUMBER;
+
+#if CONFIG_IS_ENABLED(SIFIVE_OTP)
+	struct udevice *dev;
+	int ret;
+
+	// init OTP
+	ret = uclass_get_device_by_driver(UCLASS_MISC,
+					  DM_GET_DRIVER(sifive_otp), &dev);
+
+	if (ret) {
+		debug("%s: could not find otp device\n", __func__);
+		return serial;
+	}
+
+	// read serial from OTP and set env var
+	serial = otp_read_serialnum(dev);
+#endif
+
+	return serial;
 }
 
 static void fu540_setup_macaddr(u32 serialnum)