fpga: Clarify how write_init works streaming modes

This interface was designed for streaming, but write_init's buf
argument has an unclear purpose. Define it to be the first bytes
of the bitstream. Each driver gets to set how many bytes (at most)
it wants to see. Short bitstreams will be passed through as-is, while
long ones will be truncated.

The intent is to allow drivers to peek at the header before the transfer
actually starts.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Acked-by: Alan Tull <atull@opensource.altera.com>

1 files changed, 2 insertions, 0 deletions

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,