driver: Google Memory Console

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

3 files changed, 175 insertions, 0 deletions

diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 4a0383537f5d..640dc6bedd69 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -7,3 +7,11 @@ config GOOGLE_SMI
           platforms.  This provides an interface for writing to and
           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.
diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
index fb127d7b3c7a..54a294e3cb61 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 000000000000..2a90ba613613
--- /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");