From: Marc-André Lureau <marcandre.lureau@redhat.com>

Since qemu 2.9, DMA write operations are allowed. However, usage of this
interface from kernel or user-space is strongly discouraged by the
maintainers. This patch is meant for experimentations for now.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 26152bfc7805..1ca3382e98df 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
 	return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
 }
 
+static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
+				      struct bin_attribute *bin_attr,
+				      char *buf, loff_t pos, size_t count)
+{
+	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+	if (!fw_cfg_dma_enabled())
+		return -ENOTSUPP;
+
+	if (pos > entry->f.size)
+		return -EINVAL;
+
+	if (count > entry->f.size - pos)
+		count = entry->f.size - pos;
+
+	return fw_cfg_write_blob(entry->f.select, buf, pos, count);
+}
+
 static struct bin_attribute fw_cfg_sysfs_attr_raw = {
-	.attr = { .name = "raw", .mode = S_IRUSR },
+	.attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
 	.read = fw_cfg_sysfs_read_raw,
+	.write = fw_cfg_sysfs_write_raw,
 };
 
 /*
-- 
2.14.1.146.gd35faa819