[PATCH v2 3/4] ARM: novena: Read Ethernet MAC address from EEPROM

[John Watts]

The Novena has an EEPROM used for storing information about the board,
including the Ethernet MAC address.

The reference for the EEPROM fields is the novena-eeprom source code.

Signed-off-by: John Watts <contact at jookia.org>
---
 arch/arm/boards/novena/board.c | 88 ++++++++++++++++++++++++++++++++++
 arch/arm/dts/imx6q-novena.dts  | 15 ++++++
 2 files changed, 103 insertions(+)

diff --git a/arch/arm/boards/novena/board.c b/arch/arm/boards/novena/board.c
index e247f8b8c3..24cde1c0d4 100644
--- a/arch/arm/boards/novena/board.c
+++ b/arch/arm/boards/novena/board.c
@@ -3,9 +3,97 @@
 
 #include <common.h>
 #include <deep-probe.h>
+#include <fs.h>
+#include <libfile.h>
+#include <net.h>
+
+struct novena_eeprom {
+	uint8_t signature[6]; /* 'Novena' */
+	uint8_t version; /* 1 or 2, not checked */
+	uint8_t page_size; /* v2 only: EEPROM read/write page */
+	uint32_t serial; /* 32-bit serial number */
+	uint8_t mac[6]; /* Gigabit MAC address */
+	uint16_t features; /* features */
+	/* ... extra fields omitted ... */
+} __packed;
+
+static void power_on_audio_codec(void)
+{
+	int rc = of_devices_ensure_probed_by_name("regulator-audio-codec");
+
+	if (rc < 0)
+		pr_err("Unable to power on audio codec: %s\n", strerror(-rc));
+}
+
+static struct novena_eeprom *novena_read_eeprom(void)
+{
+	size_t read;
+	loff_t max = sizeof(struct novena_eeprom);
+	void *eeprom;
+	int rc;
+
+	/*
+	 * When powered off the audio codec pulls down the EEPROM's I2C line.
+	 * Power it on so we can actually read data.
+	 */
+	power_on_audio_codec();
+
+	rc = of_device_ensure_probed_by_alias("eeprom0");
+	if (rc < 0) {
+		pr_err("Unable to probe eeprom0: %s\n", strerror(-rc));
+		return NULL;
+	}
+
+	rc = read_file_2("/dev/eeprom0", &read, &eeprom, max);
+
+	if (rc < 0 && rc != -EFBIG) {
+		pr_err("Unable to read Novena EEPROM: %s\n", strerror(-rc));
+		return NULL;
+	} else if (read != max) {
+		pr_err("Short read from Novena EEPROM?\n");
+		return NULL;
+	} else {
+		return eeprom;
+	}
+}
+
+static bool novena_check_eeprom(struct novena_eeprom *eeprom)
+{
+	char *sig = eeprom->signature;
+	size_t size = sizeof(eeprom->signature);
+
+	if (memcmp("Novena", sig, size) != 0) {
+		pr_err("Unknown Novena EEPROM signature\n");
+		return false;
+	}
+
+	return true;
+}
+
+static void novena_set_mac(struct novena_eeprom *eeprom)
+{
+	struct device_node *dnode;
+
+	dnode = of_find_node_by_alias(of_get_root_node(), "ethernet0");
+	if (dnode)
+		of_eth_register_ethaddr(dnode, eeprom->mac);
+	else
+		pr_err("Unable to find ethernet node\n");
+}
+
+static void novena_try_eeprom(void)
+{
+	struct novena_eeprom *eeprom = novena_read_eeprom();
+
+	if (!eeprom || !novena_check_eeprom(eeprom))
+		return;
+
+	novena_set_mac(eeprom);
+}
 
 static int novena_probe(struct device *dev)
 {
+	novena_try_eeprom();
+
 	return 0;
 }
 
diff --git a/arch/arm/dts/imx6q-novena.dts b/arch/arm/dts/imx6q-novena.dts
index 07471cb132..095dcde0d5 100644
--- a/arch/arm/dts/imx6q-novena.dts
+++ b/arch/arm/dts/imx6q-novena.dts
@@ -2,3 +2,18 @@
 // SPDX-FileCopyrightText: 2023 John Watts
 
 #include <arm/imx6q-novena.dts>
+
+/ {
+	aliases {
+		eeprom0 = &eeprom;
+	};
+};
+
+&i2c3 {
+	eeprom: eeprom at 56 {
+		compatible = "24c512";
+		reg = <0x56>;
+		pagesize = <128>;
+		status = "okay";
+	};
+};
-- 
2.39.0