4 files changed, 11 insertions, 3 deletions

diff --git a/Documentation/fpga/fpga-mgr.txt b/Documentation/fpga/fpga-mgr.txt
index 087924f2b20c..86ee5078fd03 100644
--- a/Documentation/fpga/fpga-mgr.txt
+++ b/Documentation/fpga/fpga-mgr.txt
@@ -169,7 +169,10 @@ The programming sequence is:
  2. .write (may be called once or multiple times)
  3. .write_complete
 
-The .write_init function will prepare the FPGA to receive the image data.
+The .write_init function will prepare the FPGA to receive the image data.  The
+buffer passed into .write_init will be atmost .initial_header_size bytes long,
+if the whole bitstream is not immediately available then the core code will
+buffer up at least this much before starting.
 
 The .write function writes a buffer to the FPGA. The buffer may be contain the
 whole FPGA image or may be a smaller chunk of an FPGA image.  In the latter
diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
index 79ce2eea44db..f0a69d3e60a5 100644
--- a/drivers/fpga/fpga-mgr.c
+++ b/drivers/fpga/fpga-mgr.c
@@ -53,10 +53,12 @@ int fpga_mgr_buf_load(struct fpga_manager *mgr, struct fpga_image_info *info,
         /*
          * Call the low level driver's write_init function.  This will do the
          * device-specific things to get the FPGA into the state where it is
-         * ready to receive an FPGA image.
+         * ready to receive an FPGA image. The low level driver only gets to
+         * see the first initial_header_size bytes in the buffer.
          */
         mgr->state = FPGA_MGR_STATE_WRITE_INIT;
-        ret = mgr->mops->write_init(mgr, info, buf, count);
+        ret = mgr->mops->write_init(mgr, info, buf,
+                                    min(mgr->mops->initial_header_size, count));
         if (ret) {
                 dev_err(dev, "Error preparing FPGA for writing\n");
                 mgr->state = FPGA_MGR_STATE_WRITE_INIT_ERR;
diff --git a/drivers/fpga/socfpga-a10.c b/drivers/fpga/socfpga-a10.c
index ccd9fb23bd52..f8770af0f6b5 100644
--- a/drivers/fpga/socfpga-a10.c
+++ b/drivers/fpga/socfpga-a10.c
@@ -470,6 +470,7 @@ static enum fpga_mgr_states socfpga_a10_fpga_state(struct fpga_manager *mgr)
 }
 
 static const struct fpga_manager_ops socfpga_a10_fpga_mgr_ops = {
+        .initial_header_size = (RBF_DECOMPRESS_OFFSET + 1) * 4,
         .state = socfpga_a10_fpga_state,
         .write_init = socfpga_a10_fpga_write_init,
         .write = socfpga_a10_fpga_write,
diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index 96a1a3311649..16551d5eac36 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -84,6 +84,7 @@ struct fpga_image_info {
 
 /**
  * struct fpga_manager_ops - ops for low level fpga manager drivers
+ * @initial_header_size: Maximum number of bytes that should be passed into write_init
  * @state: returns an enum value of the FPGA's state
  * @write_init: prepare the FPGA to receive confuration data
  * @write: write count bytes of configuration data to the FPGA
@@ -95,6 +96,7 @@ struct fpga_image_info {
  * called, so leaving them out is fine.
  */
 struct fpga_manager_ops {
+        size_t initial_header_size;
         enum fpga_mgr_states (*state)(struct fpga_manager *mgr);
         int (*write_init)(struct fpga_manager *mgr,
                           struct fpga_image_info *info,