firmware: google memconsole: Add coreboot support

Coreboot (http://www.coreboot.org) allows to save the firmware console
output in a memory buffer. With this patch, the address of this memory
buffer is obtained from coreboot tables on x86 chromebook devices
declaring an ACPI device with name matching GOOGCB00 or BOOT0000.

If the memconsole-coreboot driver is able to find the coreboot table,
the memconsole driver sets the cbmem_console address and initializes the
memconsole sysfs entries.

The coreboot_table-acpi driver is responsible for setting the address of
the coreboot table header when probed. If this address is not yet set
when memconsole-coreboot is probed, then the probe is deferred by
returning -EPROBE_DEFER.

This patch is a rework/split/merge of patches from the chromeos v4.4
kernel tree originally authored by:
 Vadim Bendebury <vbendeb@chromium.org>
 Wei-Ning Huang <wnhuang@google.com>
 Yuji Sasaki <sasakiy@google.com>
 Duncan Laurie <dlaurie@chromium.org>
 Julius Werner <jwerner@chromium.org>
 Brian Norris <briannorris@chromium.org>

Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 94 insertions, 0 deletions

diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
new file mode 100644
index 000000000000..0019d3ec18dd
--- /dev/null
+++ b/drivers/firmware/google/coreboot_table.c
@@ -0,0 +1,94 @@
+/*
+ * coreboot_table.c
+ *
+ * Module providing coreboot table access.
+ *
+ * Copyright 2017 Google Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License v2.0 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#include "coreboot_table.h"
+
+struct coreboot_table_entry {
+	u32 tag;
+	u32 size;
+};
+
+static struct coreboot_table_header __iomem *ptr_header;
+
+/*
+ * This function parses the coreboot table for an entry that contains the base
+ * address of the given entry tag. The coreboot table consists of a header
+ * directly followed by a number of small, variable-sized entries, which each
+ * contain an identifying tag and their length as the first two fields.
+ */
+int coreboot_table_find(int tag, void *data, size_t data_size)
+{
+	struct coreboot_table_header header;
+	struct coreboot_table_entry entry;
+	void *ptr_entry;
+	int i;
+
+	if (!ptr_header)
+		return -EPROBE_DEFER;
+
+	memcpy_fromio(&header, ptr_header, sizeof(header));
+
+	if (strncmp(header.signature, "LBIO", sizeof(header.signature))) {
+		pr_warn("coreboot_table: coreboot table missing or corrupt!\n");
+		return -ENODEV;
+	}
+
+	ptr_entry = (void *)ptr_header + header.header_bytes;
+
+	for (i = 0; i < header.table_entries; i++) {
+		memcpy_fromio(&entry, ptr_entry, sizeof(entry));
+		if (entry.tag == tag) {
+			if (data_size < entry.size)
+				return -EINVAL;
+
+			memcpy_fromio(data, ptr_entry, entry.size);
+
+			return 0;
+		}
+
+		ptr_entry += entry.size;
+	}
+
+	return -ENOENT;
+}
+EXPORT_SYMBOL(coreboot_table_find);
+
+int coreboot_table_init(void __iomem *ptr)
+{
+	ptr_header = ptr;
+
+	return 0;
+}
+EXPORT_SYMBOL(coreboot_table_init);
+
+int coreboot_table_exit(void)
+{
+	if (ptr_header)
+		iounmap(ptr_header);
+
+	return 0;
+}
+EXPORT_SYMBOL(coreboot_table_exit);
+
+MODULE_AUTHOR("Google, Inc.");
+MODULE_LICENSE("GPL");