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fpga: Clarify how write_init works streaming modes

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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>
This commit is contained in:
Jason Gunthorpe 2016-11-22 18:22:09 +00:00 • committed by Alan Tull
parent 340c0c53ea
commit 1d7f1589d3
4 changed files with 11 additions and 3 deletions
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5
Documentation/fpga/fpga-mgr.txt
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@ -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