[doc] Possible error(s) in SPI Device HWIP Technical Specification - Block Diagram

[jonmccune]

Public page: https://docs.opentitan.org/hw/ip/spi_device/doc/
Public direct link to the problematic diagram: https://docs.opentitan.org/hw/ip/spi_device/doc/block_diagram.svg
Github code link: https://github.com/lowRISC/opentitan/blob/master/hw/ip/spi_device/doc/block_diagram.svg

Empty search for known issues:
https://github.com/lowRISC/opentitan/issues?q=is%3Aissue+block_diagram.svg

I notice a few issues with this diagram. I don't think this is exhaustive - hopefully an expert can make a pass.

• Should the TX FIFO be directional? Right now it has arrows going both directions.
• Should the Arbiter have a bi-directional arrow to DP_SRAM?
• Are the "Serial to Parallel" and "Parallel to Serial" boxes reversed?

[andreaskurth]

Triaged for spi_device. Assigning to M2.5 with Priority:P4 Priority: propose to move to backlog because I think this is worth keeping in mind on spi_device, but we can fix this after M2.5.

[hcallahan-lowrisc]

estimate 2
remaining 2023-03-22 2

[a-will]

Looks like these were for an older block diagram (the s2p and p2s blocks are getting into the noise, and they aren't present anymore, for example). Closing...