tests: drivers: smbus: add packet error correction (pec) testsuite

Add tests for SMBus packet error correction (PEC). The two primary
utilities tested are

* smbus_pec(): compute the PEC byte for a Block Write
* smbus_read_check_pec(): verify a PEC after
  * Read Byte
  * Read Word
  * Block Read

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

tests/drivers/smbus/smbus_pec/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (c) 2025 Tenstorrent AI ULC
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(smbus_pec)
+
+target_include_directories(app PRIVATE ${ZEPHYR_BASE}/drivers/smbus)
+
+target_sources(app PRIVATE src/main.c)

tests/drivers/smbus/smbus_pec/prj.conf

@@ -0,0 +1,4 @@
+CONFIG_ZTEST=y
+
+CONFIG_SMBUS=y
+CONFIG_SMBUS_SOFT_PEC=y

tests/drivers/smbus/smbus_pec/src/main.c

@@ -0,0 +1,133 @@
+/*
+ * Copyright (c) 2025 Tenstorrent AI ULC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/ztest.h>
+#include <zephyr/sys/util.h>
+
+#include <smbus_utils.h>
+
+ZTEST(smbus_pec, test_smbus_pec)
+{
+	uint8_t addr = 0x42;
+	/* Write Block with PEC (SMBus spec v3.1, Section 6.5.7) */
+	uint8_t write_data[] = {
+		0x73, /* command */
+		4, /* len */
+		0xde, 0xad, 0xbe, 0xef, /* data */
+	};
+	struct i2c_msg msgs[] = {
+		{
+			.buf = write_data,
+			.len = sizeof(write_data),
+			.flags = I2C_MSG_WRITE | I2C_MSG_STOP,
+		},
+		/* driver would add a PEC message here */
+	};
+
+	uint8_t actual_pec = smbus_pec(addr, msgs, ARRAY_SIZE(msgs));
+	uint8_t expected_pec = 0x12;
+
+	zexpect_equal(expected_pec, actual_pec, "expected: %02x actual: %02x",
+		      expected_pec, actual_pec);
+}
+
+ZTEST(smbus_pec, test_smbus_read_check_pec)
+{
+	uint8_t addr = 0xa;
+
+	{
+		/* Read Byte with PEC (SMBus spec v3.1, Section 6.5.5) */
+		uint8_t data[] = {
+			0x10, /* command */
+			0x05, /* data */
+			0x90, /* PEC */
+		};
+		struct i2c_msg msgs[] = {
+			{
+				.buf = &data[0], /* command */
+				.len = 1,
+				.flags = I2C_MSG_WRITE,
+			},
+			{
+				.buf = &data[1], /* data */
+				.len = 1,
+				.flags = I2C_MSG_READ,
+			},
+			{
+				.buf = &data[2], /* PEC */
+				.len = 1,
+				.flags = I2C_MSG_READ,
+			},
+		};
+
+		zexpect_ok(smbus_read_check_pec(SMBUS_MODE_PEC, addr, msgs, ARRAY_SIZE(msgs)));
+	}
+
+	{
+		/* Read Word with PEC (SMBus spec v3.1, Section 6.5.5) */
+		uint8_t data[] = {
+			0x10, /* command */
+			0x05, /* data byte (low) */
+			0x0a, /* data byte (high) */
+			0xcf, /* PEC */
+		};
+		struct i2c_msg msgs[] = {
+			{
+				.buf = &data[0], /* command */
+				.len = 1,
+				.flags = I2C_MSG_WRITE,
+			},
+			{
+				.buf = &data[1], /* data */
+				.len = 2,
+				.flags = I2C_MSG_READ,
+			},
+			{
+				.buf = &data[3], /* PEC */
+				.len = 1,
+				.flags = I2C_MSG_READ,
+			},
+		};
+
+		zexpect_ok(smbus_read_check_pec(SMBUS_MODE_PEC, addr, msgs, ARRAY_SIZE(msgs)));
+	}
+
+	{
+		/* Block read (SMBus spec v3.1, Section 6.5.7) */
+		uint8_t data[] = {
+			0x10,                               /* command */
+			0x06,                               /* block count */
+			0x05, 0x00, 0x00, 0x00, 0x00, 0x00, /* data */
+			0x99,                               /* PEC */
+		};
+		struct i2c_msg msgs[] = {
+			{
+				.buf = &data[0], /* command */
+				.len = 1,
+				.flags = I2C_MSG_WRITE,
+			},
+			{
+				.buf = &data[1], /* block count */
+				.len = 1,
+				.flags = I2C_MSG_READ | I2C_MSG_RESTART,
+			},
+			{
+				.buf = &data[2], /* data */
+				.len = data[1],
+				.flags = I2C_MSG_READ,
+			},
+			{
+				.buf = &data[2] + data[1], /* PEC */
+				.len = 1,
+				.flags = I2C_MSG_READ,
+			},
+		};
+
+		zexpect_ok(smbus_read_check_pec(SMBUS_MODE_PEC, addr, msgs, ARRAY_SIZE(msgs)));
+	}
+}
+
+ZTEST_SUITE(smbus_pec, NULL, NULL, NULL, NULL, NULL);

tests/drivers/smbus/smbus_pec/testcase.yaml

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+common:
+  tags: smbus
+tests:
+  drivers.smbus.pec: {}