x86, AMD IOMMU: add command buffer (de-)allocation

This patch adds the functions to allocate and deallocate the command buffer for
one IOMMU in the system.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: Sebastian.Biemueller@amd.com
Cc: robert.richter@amd.com
Cc: joro@8bytes.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/amd_iommu_init.c

@@ -278,3 +278,33 @@ static int __init find_last_devid_acpi(struct acpi_table_header *table)
 	return 0;
 }
 
+static u8 * __init alloc_command_buffer(struct amd_iommu *iommu)
+{
+	u8 *cmd_buf = (u8 *)__get_free_pages(GFP_KERNEL,
+			get_order(CMD_BUFFER_SIZE));
+	u64 entry = 0;
+
+	if (cmd_buf == NULL)
+		return NULL;
+
+	iommu->cmd_buf_size = CMD_BUFFER_SIZE;
+
+	memset(cmd_buf, 0, CMD_BUFFER_SIZE);
+
+	entry = (u64)virt_to_phys(cmd_buf);
+	entry |= MMIO_CMD_SIZE_512;
+	memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET,
+			&entry, sizeof(entry));
+
+	iommu_feature_enable(iommu, CONTROL_CMDBUF_EN);
+
+	return cmd_buf;
+}
+
+static void __init free_command_buffer(struct amd_iommu *iommu)
+{
+	if (iommu->cmd_buf)
+		free_pages((unsigned long)iommu->cmd_buf,
+				get_order(CMD_BUFFER_SIZE));
+}
+