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Subject[PATCH v3 5/5] driver: Google Memory Console
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This patch introduces the 'memconsole' driver.

Our firmware gives us access to an in-memory log of the firmware's
output. This gives us visibility in a data-center of headless machines
as to what the firmware is doing.

The memory console is found by the driver by finding a header block in
the EBDA. The buffer is then copied out, and is exported to userland in
the file /sys/firmware/log.

Signed-off-by: San Mehat <san@google.com>
Signed-off-by: Mike Waychison <mikew@google.com>
---
Changelog:
v3:
- Use dmi_check_system to only load when on a Google board.
- Use MODULE_DEVICE_TABLE to export matching DMI strings.
- Default to 'n' in the Kconfig.
- Fixed Kconfig description to reflect that this change no longer
messes with the dmesg.
v2:
- Removed bits that had this driver muck with the kernel's ring
dmesg buffer (log_buf).
- Introduced the log as /sys/firmware/log, a binary file that isn't
interpreted by the kernel.
- Don't use C99 fixed width types; use kernel fixed width types.
- Added file to Documentation/ABI for /sys/firmware/log
---
Documentation/ABI/testing/sysfs-firmware-log | 7 +
drivers/firmware/google/Kconfig | 8 +
drivers/firmware/google/Makefile | 1
drivers/firmware/google/memconsole.c | 166 ++++++++++++++++++++++++++
4 files changed, 182 insertions(+), 0 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-firmware-log
create mode 100644 drivers/firmware/google/memconsole.c
diff --git a/Documentation/ABI/testing/sysfs-firmware-log b/Documentation/ABI/testing/sysfs-firmware-log
new file mode 100644
index 0000000..9b58e7c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-log
@@ -0,0 +1,7 @@
+What: /sys/firmware/log
+Date: February 2011
+Contact: Mike Waychison <mikew@google.com>
+Description:
+ The /sys/firmware/log is a binary file that represents a
+ read-only copy of the firmware's log if one is
+ available.
diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 8190103..87096b6 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -20,4 +20,12 @@ config GOOGLE_SMI
clearing the EFI event log and reading and writing NVRAM
variables.

+config GOOGLE_MEMCONSOLE
+ tristate "Firmware Memory Console"
+ depends on DMI
+ help
+ This option enables the kernel to search for a firmware log in
+ the EBDA on Google servers. If found, this log is exported to
+ userland in the file /sys/firmware/log.
+
endmenu
diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
index fb127d7..54a294e 100644
--- a/drivers/firmware/google/Makefile
+++ b/drivers/firmware/google/Makefile
@@ -1,2 +1,3 @@

obj-$(CONFIG_GOOGLE_SMI) += gsmi.o
+obj-$(CONFIG_GOOGLE_MEMCONSOLE) += memconsole.o
diff --git a/drivers/firmware/google/memconsole.c b/drivers/firmware/google/memconsole.c
new file mode 100644
index 0000000..2a90ba6
--- /dev/null
+++ b/drivers/firmware/google/memconsole.c
@@ -0,0 +1,166 @@
+/*
+ * memconsole.c
+ *
+ * Infrastructure for importing the BIOS memory based console
+ * into the kernel log ringbuffer.
+ *
+ * Copyright 2010 Google Inc. All rights reserved.
+ */
+
+#include <linux/ctype.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+#include <linux/dmi.h>
+#include <asm/bios_ebda.h>
+
+#define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE
+#define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24))
+
+struct biosmemcon_ebda {
+ u32 signature;
+ union {
+ struct {
+ u8 enabled;
+ u32 buffer_addr;
+ u16 start;
+ u16 end;
+ u16 num_chars;
+ u8 wrapped;
+ } __packed v1;
+ struct {
+ u32 buffer_addr;
+ /* Misdocumented as number of pages! */
+ u16 num_bytes;
+ u16 start;
+ u16 end;
+ } __packed v2;
+ };
+} __packed;
+
+static char *memconsole_baseaddr;
+static size_t memconsole_length;
+
+static ssize_t memconsole_read(struct file *filp, struct kobject *kobp,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t pos, size_t count)
+{
+ return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
+ memconsole_length);
+}
+
+static struct bin_attribute memconsole_bin_attr = {
+ .attr = {.name = "log", .mode = 0444},
+ .read = memconsole_read,
+};
+
+
+static void found_v1_header(struct biosmemcon_ebda *hdr)
+{
+ printk(KERN_INFO "BIOS console v1 EBDA structure found at %p\n", hdr);
+ printk(KERN_INFO "BIOS console buffer at 0x%.8x, "
+ "start = %d, end = %d, num = %d\n",
+ hdr->v1.buffer_addr, hdr->v1.start,
+ hdr->v1.end, hdr->v1.num_chars);
+
+ memconsole_length = hdr->v1.num_chars;
+ memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
+}
+
+static void found_v2_header(struct biosmemcon_ebda *hdr)
+{
+ printk(KERN_INFO "BIOS console v2 EBDA structure found at %p\n", hdr);
+ printk(KERN_INFO "BIOS console buffer at 0x%.8x, "
+ "start = %d, end = %d, num_bytes = %d\n",
+ hdr->v2.buffer_addr, hdr->v2.start,
+ hdr->v2.end, hdr->v2.num_bytes);
+
+ memconsole_length = hdr->v2.end - hdr->v2.start;
+ memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr
+ + hdr->v2.start);
+}
+
+/*
+ * Search through the EBDA for the BIOS Memory Console, and
+ * set the global variables to point to it. Return true if found.
+ */
+static bool found_memconsole(void)
+{
+ unsigned int address;
+ size_t length, cur;
+
+ address = get_bios_ebda();
+ if (!address) {
+ printk(KERN_INFO "BIOS EBDA non-existent.\n");
+ return false;
+ }
+
+ /* EBDA length is byte 0 of EBDA (in KB) */
+ length = *(u8 *)phys_to_virt(address);
+ length <<= 10; /* convert to bytes */
+
+ /*
+ * Search through EBDA for BIOS memory console structure
+ * note: signature is not necessarily dword-aligned
+ */
+ for (cur = 0; cur < length; cur++) {
+ struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
+
+ /* memconsole v1 */
+ if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
+ found_v1_header(hdr);
+ return true;
+ }
+
+ /* memconsole v2 */
+ if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
+ found_v2_header(hdr);
+ return true;
+ }
+ }
+
+ printk(KERN_INFO "BIOS console EBDA structure not found!\n");
+ return false;
+}
+
+static struct dmi_system_id memconsole_dmi_table[] __initdata = {
+ {
+ .ident = "Google Board",
+ .matches = {
+ DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
+ },
+ },
+ {}
+};
+MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
+
+static int __init memconsole_init(void)
+{
+ int ret;
+
+ if (!dmi_check_system(memconsole_dmi_table))
+ return -ENODEV;
+
+ if (!found_memconsole())
+ return -ENODEV;
+
+ memconsole_bin_attr.size = memconsole_length;
+
+ ret = sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr);
+
+ return ret;
+}
+
+static void __exit memconsole_exit(void)
+{
+ sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr);
+}
+
+module_init(memconsole_init);
+module_exit(memconsole_exit);
+
+MODULE_AUTHOR("Google, Inc.");
+MODULE_LICENSE("GPL");


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