[flash_ctrl] Pop read pipeline FIFOs for data and mask in sync #22571
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This commit fixes a bug in the read pipeline where the data and the mask storage FIFO could get out of sync in case of the mask computation running behind the actual Flash read (e.g. due to back pressure in the shared scrambling logic). To avoid the FIFOs getting out of sync, the design now tracks whether for reads that don't require descrambling, a mask was still computed. This can happen if for scramble enabled locations that are being erased. In case a mask computation has been started, the FIFOs are now only popped if both the data and the mask FIFO contain a valid entry (i.e. the mask computation for the data to be popped has finished). This resolves lowRISC#22443 Signed-off-by: Pirmin Vogel <[email protected]>
matutem
approved these changes
Apr 16, 2024
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Thanks @matutem ! Regarding implementing a state machine for this: I don't know if this would improve things to be honest as the read pipeline is pipelined: Multiple requests can be in flight and there is even a small cache. I believe this is always going to be a bit messy. What would maybe help is a more thorough cleanup (of code and comments - some are no longer aligned with the RTL) but I fear this would introduce risk again which is undesirable at this stage. |
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Regression results are here, things look good: |
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This commit fixes a bug in the read pipeline where the data and the mask storage FIFO could get out of sync in case of the mask computation running behind the actual Flash read (e.g. due to back pressure in the shared scrambling logic).
To avoid the FIFOs getting out of sync, the design now tracks whether for reads that don't require descrambling, a mask was still computed. This can happen if for scramble enabled locations that are being erased. In case a mask computation has been started, the FIFOs are now only popped if both the data and the mask FIFO contain a valid entry (i.e. the mask computation for the data to be popped has finished).
This resolves #22443