Add an I/O tracing feature

When debugging drivers it is useful to see what I/O accesses were done
and in what order.

Even if the individual accesses are of little interest it can be useful to
verify that the access pattern is consistent each time an operation is
performed. In this case a checksum can be used to characterise the operation
of a driver. The checksum can be compared across different runs of the
operation to verify that the driver is working properly.

In particular, when performing major refactoring of the driver, where the
access pattern should not change, the checksum provides assurance that the
refactoring work has not broken the driver.

Add an I/O tracing feature and associated commands to provide this facility.
It works by sneaking into the io.h heder for an architecture and redirecting
I/O accesses through its tracing mechanism.

For now no commands are provided to examine the trace buffer. The format is
fairly simple, so 'md' is a reasonable substitute.

Note: The checksum feature is only useful for I/O regions where the contents
do not change outside of software control. Where this is not suitable you can
fall back to manually comparing the addresses. It might be useful to enhance
tracing to only checksum the accesses and not the data read/written.

Signed-off-by: Simon Glass <sjg@chromium.org>

README

@@ -1000,6 +1000,7 @@ The following options need to be configured:
 		CONFIG_CMD_IMLS		  List all images found in NOR flash
 		CONFIG_CMD_IMLS_NAND	* List all images found in NAND flash
 		CONFIG_CMD_IMMAP	* IMMR dump support
+		CONFIG_CMD_IOTRACE	* I/O tracing for debugging
 		CONFIG_CMD_IMPORTENV	* import an environment
 		CONFIG_CMD_INI		* import data from an ini file into the env
 		CONFIG_CMD_IRQ		* irqinfo
@@ -1171,6 +1172,28 @@ The following options need to be configured:
 		Note that if the GPIO device uses I2C, then the I2C interface
 		must also be configured. See I2C Support, below.
 
+- I/O tracing:
+		When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
+		accesses and can checksum them or write a list of them out
+		to memory. See the 'iotrace' command for details. This is
+		useful for testing device drivers since it can confirm that
+		the driver behaves the same way before and after a code
+		change. Currently this is supported on sandbox and arm. To
+		add support for your architecture, add '#include <iotrace.h>'
+		to the bottom of arch/<arch>/include/asm/io.h and test.
+
+		Example output from the 'iotrace stats' command is below.
+		Note that if the trace buffer is exhausted, the checksum will
+		still continue to operate.
+
+			iotrace is enabled
+			Start:  10000000	(buffer start address)
+			Size:   00010000	(buffer size)
+			Offset: 00000120	(current buffer offset)
+			Output: 10000120	(start + offset)
+			Count:  00000018	(number of trace records)
+			CRC32:  9526fb66	(CRC32 of all trace records)
+
 - Timestamp Support:
 
 		When CONFIG_TIMESTAMP is selected, the timestamp

common/Makefile

@@ -114,6 +114,7 @@ obj-$(CONFIG_CMD_FUSE) += cmd_fuse.o
 obj-$(CONFIG_CMD_GETTIME) += cmd_gettime.o
 obj-$(CONFIG_CMD_GPIO) += cmd_gpio.o
 obj-$(CONFIG_CMD_I2C) += cmd_i2c.o
+obj-$(CONFIG_CMD_IOTRACE) += cmd_iotrace.o
 obj-$(CONFIG_CMD_HASH) += cmd_hash.o
 obj-$(CONFIG_CMD_IDE) += cmd_ide.o
 obj-$(CONFIG_CMD_IMMAP) += cmd_immap.o
@@ -261,6 +262,7 @@ obj-$(CONFIG_ANDROID_BOOT_IMAGE) += image-android.o
 obj-$(CONFIG_OF_LIBFDT) += image-fdt.o
 obj-$(CONFIG_FIT) += image-fit.o
 obj-$(CONFIG_FIT_SIGNATURE) += image-sig.o
+obj-$(CONFIG_IO_TRACE) += iotrace.o
 obj-y += memsize.o
 obj-y += stdio.o
 

common/cmd_iotrace.c

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2014 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <command.h>
+#include <iotrace.h>
+
+static void do_print_stats(void)
+{
+	ulong start, size, offset, count;
+
+	printf("iotrace is %sabled\n", iotrace_get_enabled() ? "en" : "dis");
+	iotrace_get_buffer(&start, &size, &offset, &count);
+	printf("Start:  %08lx\n", start);
+	printf("Size:   %08lx\n", size);
+	printf("Offset: %08lx\n", offset);
+	printf("Output: %08lx\n", start + offset);
+	printf("Count:  %08lx\n", count);
+	printf("CRC32:  %08lx\n", (ulong)iotrace_get_checksum());
+}
+
+static int do_set_buffer(int argc, char * const argv[])
+{
+	ulong addr = 0, size = 0;
+
+	if (argc == 2) {
+		addr = simple_strtoul(*argv++, NULL, 16);
+		size = simple_strtoul(*argv++, NULL, 16);
+	} else if (argc != 0) {
+		return CMD_RET_USAGE;
+	}
+
+	iotrace_set_buffer(addr, size);
+
+	return 0;
+}
+
+int do_iotrace(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	const char *cmd = argc < 2 ? NULL : argv[1];
+
+	if (!cmd)
+		return cmd_usage(cmdtp);
+	switch (*cmd) {
+	case 'b':
+		return do_set_buffer(argc - 2, argv + 2);
+	case 'p':
+		iotrace_set_enabled(0);
+		break;
+	case 'r':
+		iotrace_set_enabled(1);
+		break;
+	case 's':
+		do_print_stats();
+		break;
+	default:
+		return CMD_RET_USAGE;
+	}
+
+	return 0;
+}
+
+U_BOOT_CMD(
+	iotrace,	4,	1,	do_iotrace,
+	"iotrace utility commands",
+	"stats                        - display iotrace stats\n"
+	"iotrace buffer <address> <size>      - set iotrace buffer\n"
+	"iotrace pause                        - pause tracing\n"
+	"iotrace resume                       - resume tracing"
+);

common/iotrace.c

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2014 Google, Inc.
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#define IOTRACE_IMPL
+
+#include <common.h>
+#include <asm/io.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+/* Support up to the machine word length for now */
+typedef ulong iovalue_t;
+
+enum iotrace_flags {
+	IOT_8 = 0,
+	IOT_16,
+	IOT_32,
+
+	IOT_READ = 0 << 3,
+	IOT_WRITE = 1 << 3,
+};
+
+/**
+ * struct iotrace_record - Holds a single I/O trace record
+ *
+ * @flags: I/O access type
+ * @addr: Address of access
+ * @value: Value written or read
+ */
+struct iotrace_record {
+	enum iotrace_flags flags;
+	phys_addr_t addr;
+	iovalue_t value;
+};
+
+/**
+ * struct iotrace - current trace status and checksum
+ *
+ * @start:	Start address of iotrace buffer
+ * @size:	Size of iotrace buffer in bytes
+ * @offset:	Current write offset into iotrace buffer
+ * @crc32:	Current value of CRC chceksum of trace records
+ * @enabled:	true if enabled, false if disabled
+ */
+static struct iotrace {
+	ulong start;
+	ulong size;
+	ulong offset;
+	u32 crc32;
+	bool enabled;
+} iotrace;
+
+static void add_record(int flags, const void *ptr, ulong value)
+{
+	struct iotrace_record srec, *rec = &srec;
+
+	/*
+	 * We don't support iotrace before relocation. Since the trace buffer
+	 * is set up by a command, it can't be enabled at present. To change
+	 * this we would need to set the iotrace buffer at build-time. See
+	 * lib/trace.c for how this might be done if you are interested.
+	 */
+	if (!(gd->flags & GD_FLG_RELOC) || !iotrace.enabled)
+		return;
+
+	/* Store it if there is room */
+	if (iotrace.offset + sizeof(*rec) < iotrace.size) {
+		rec = (struct iotrace_record *)map_sysmem(
+					iotrace.start + iotrace.offset,
+					sizeof(value));
+	}
+
+	rec->flags = flags;
+	rec->addr = map_to_sysmem(ptr);
+	rec->value = value;
+
+	/* Update our checksum */
+	iotrace.crc32 = crc32(iotrace.crc32, (unsigned char *)rec,
+			      sizeof(*rec));
+
+	iotrace.offset += sizeof(struct iotrace_record);
+}
+
+u32 iotrace_readl(const void *ptr)
+{
+	u32 v;
+
+	v = readl(ptr);
+	add_record(IOT_32 | IOT_READ, ptr, v);
+
+	return v;
+}
+
+void iotrace_writel(ulong value, const void *ptr)
+{
+	add_record(IOT_32 | IOT_WRITE, ptr, value);
+	writel(value, ptr);
+}
+
+u16 iotrace_readw(const void *ptr)
+{
+	u32 v;
+
+	v = readw(ptr);
+	add_record(IOT_16 | IOT_READ, ptr, v);
+
+	return v;
+}
+
+void iotrace_writew(ulong value, const void *ptr)
+{
+	add_record(IOT_16 | IOT_WRITE, ptr, value);
+	writew(value, ptr);
+}
+
+u8 iotrace_readb(const void *ptr)
+{
+	u32 v;
+
+	v = readb(ptr);
+	add_record(IOT_8 | IOT_READ, ptr, v);
+
+	return v;
+}
+
+void iotrace_writeb(ulong value, const void *ptr)
+{
+	add_record(IOT_8 | IOT_WRITE, ptr, value);
+	writeb(value, ptr);
+}
+
+void iotrace_reset_checksum(void)
+{
+	iotrace.crc32 = 0;
+}
+
+u32 iotrace_get_checksum(void)
+{
+	return iotrace.crc32;
+}
+
+void iotrace_set_enabled(int enable)
+{
+	iotrace.enabled = enable;
+}
+
+int iotrace_get_enabled(void)
+{
+	return iotrace.enabled;
+}
+
+void iotrace_set_buffer(ulong start, ulong size)
+{
+	iotrace.start = start;
+	iotrace.size = size;
+	iotrace.offset = 0;
+	iotrace.crc32 = 0;
+}
+
+void iotrace_get_buffer(ulong *start, ulong *size, ulong *offset, ulong *count)
+{
+	*start = iotrace.start;
+	*size = iotrace.size;
+	*offset = iotrace.offset;
+	*count = iotrace.offset / sizeof(struct iotrace_record);
+}

include/iotrace.h

@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2014 Google, Inc.
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#ifndef __IOTRACE_H
+#define __IOTRACE_H
+
+#include <linux/types.h>
+
+/*
+ * This file is designed to be included in arch/<arch>/include/asm/io.h.
+ * It redirects all IO access through a tracing/checksumming feature for
+ * testing purposes.
+ */
+
+#if defined(CONFIG_IO_TRACE) && !defined(IOTRACE_IMPL) && \
+	!defined(CONFIG_SPL_BUILD)
+
+#undef readl
+#define readl(addr)	iotrace_readl((const void *)(addr))
+
+#undef writel
+#define writel(val, addr)	iotrace_writel(val, (const void *)(addr))
+
+#undef readw
+#define readw(addr)	iotrace_readw((const void *)(addr))
+
+#undef writew
+#define writew(val, addr)	iotrace_writew(val, (const void *)(addr))
+
+#undef readb
+#define readb(addr)	iotrace_readb((const void *)(addr))
+
+#undef writeb
+#define writeb(val, addr)	iotrace_writeb(val, (const void *)(addr))
+
+#endif
+
+/* Tracing functions which mirror their io.h counterparts */
+u32 iotrace_readl(const void *ptr);
+void iotrace_writel(ulong value, const void *ptr);
+u16 iotrace_readw(const void *ptr);
+void iotrace_writew(ulong value, const void *ptr);
+u8 iotrace_readb(const void *ptr);
+void iotrace_writeb(ulong value, const void *ptr);
+
+/**
+ * iotrace_reset_checksum() - Reset the iotrace checksum
+ */
+void iotrace_reset_checksum(void);
+
+/**
+ * iotrace_get_checksum() - Get the current checksum value
+ *
+ * @return currect checksum value
+ */
+u32 iotrace_get_checksum(void);
+
+/**
+ * iotrace_set_enabled() - Set whether iotracing is enabled or not
+ *
+ * This controls whether the checksum is updated and a trace record added
+ * for each I/O access.
+ *
+ * @enable: true to enable iotracing, false to disable
+ */
+void iotrace_set_enabled(int enable);
+
+/**
+ * iotrace_get_enabled() - Get whether iotracing is enabled or not
+ *
+ * @return true if enabled, false if disabled
+ */
+int iotrace_get_enabled(void);
+
+/**
+ * iotrace_set_buffer() - Set position and size of iotrace buffer
+ *
+ * Defines where the iotrace buffer goes, and resets the output pointer to
+ * the start of the buffer.
+ *
+ * The buffer can be 0 size in which case the checksum is updated but no
+ * trace records are writen. If the buffer is exhausted, the offset will
+ * continue to increase but not new data will be written.
+ *
+ * @start: Start address of buffer
+ * @size: Size of buffer in bytes
+ */
+void iotrace_set_buffer(ulong start, ulong size);
+
+/**
+ * iotrace_get_buffer() - Get buffer information
+ *
+ * @start: Returns start address of buffer
+ * @size: Returns size of buffer in bytes
+ * @offset: Returns the byte offset where the next output trace record will
+ * @count: Returns the number of trace records recorded
+ * be written (or would be if the buffer was large enough)
+ */
+void iotrace_get_buffer(ulong *start, ulong *size, ulong *offset, ulong *count);
+
+#endif /* __IOTRACE_H */