[PATCH v4 10/21] acpi/table: Introduce acpi_table_get_entry_madt to get specified entry

[Shannon Zhao <zhaoshenglong@huawei.com>]

From: Shannon Zhao <shannon.zhao@linaro.org>

This function could get the specified index entry of MADT table. This
would be useful when it needs to get the contens of the entry.

Cc: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
---
V4: Fix coding style and make the function only for MADT table
---
 xen/drivers/acpi/tables.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/acpi.h    |  2 ++
 2 files changed, 61 insertions(+)

diff --git a/xen/drivers/acpi/tables.c b/xen/drivers/acpi/tables.c
index 84a290f..c50bae4 100644
--- a/xen/drivers/acpi/tables.c
+++ b/xen/drivers/acpi/tables.c
@@ -219,6 +219,65 @@ void __init acpi_table_print_madt_entry(struct acpi_subtable_header *header)
 	}
 }
 
+static struct acpi_subtable_header * __init
+acpi_get_entry(char *id, unsigned long table_size,
+	       struct acpi_table_header *table_header, int entry_id,
+	       unsigned int entry_index)
+{
+	struct acpi_subtable_header *entry;
+	int count = 0;
+	unsigned long table_end;
+
+	if (!table_size)
+		return NULL;
+
+	if (!table_header) {
+		printk(KERN_WARNING PREFIX "%4.4s not present\n", id);
+		return NULL;
+	}
+
+	table_end = (unsigned long)table_header + table_header->length;
+
+	/* Parse all entries looking for a match. */
+	entry = (struct acpi_subtable_header *)
+	    ((unsigned long)table_header + table_size);
+
+	while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) <
+	       table_end) {
+		if (entry->length < sizeof(*entry)) {
+			printk(KERN_ERR PREFIX "[%4.4s:%#x] Invalid length\n",
+			       id, entry_id);
+			return NULL;
+		}
+
+		if (entry->type == entry_id) {
+			if (count == entry_index)
+				return entry;
+			count++;
+		}
+
+		entry = (struct acpi_subtable_header *)
+		    ((unsigned long)entry + entry->length);
+	}
+
+	return NULL;
+}
+
+struct acpi_subtable_header * __init
+acpi_table_get_entry_madt(enum acpi_madt_type id, unsigned int entry_index)
+{
+	struct acpi_table_header *table_header = NULL;
+
+	acpi_get_table(ACPI_SIG_MADT, acpi_apic_instance, &table_header);
+	if (!table_header) {
+		printk(KERN_WARNING PREFIX "%4.4s not present\n",
+		       ACPI_SIG_MADT);
+		return NULL;
+	}
+
+	return acpi_get_entry(ACPI_SIG_MADT, sizeof(struct acpi_table_madt),
+			      table_header, id, entry_index);
+}
 
 int __init
 acpi_parse_entries(char *id, unsigned long table_size,
diff --git a/xen/include/xen/acpi.h b/xen/include/xen/acpi.h
index bc73310..32d7a4f 100644
--- a/xen/include/xen/acpi.h
+++ b/xen/include/xen/acpi.h
@@ -74,6 +74,8 @@ int acpi_parse_entries(char *id, unsigned long table_size,
 		       int entry_id, unsigned int max_entries);
 int acpi_table_parse_entries(char *id, unsigned long table_size,
 	int entry_id, acpi_table_entry_handler handler, unsigned int max_entries);
+struct acpi_subtable_header *acpi_table_get_entry_madt(enum acpi_madt_type id,
+						      unsigned int entry_index);
 int acpi_table_parse_madt(enum acpi_madt_type id, acpi_table_entry_handler handler, unsigned int max_entries);
 int acpi_table_parse_srat(int id, acpi_madt_entry_handler handler,
 	unsigned int max_entries);
-- 
2.0.4