High-Speed Synchronous Serial Interface (HSI) bus framework
A bus framework for the High-Speed Synchronous Serial Interface, a short-distance serial link used inside smartphones to connect an application processor to a cellular modem. The only in-tree users are TI's OMAP SSI controller and the modem on Nokia's 2009-era N900.
recommendation
Worth keeping but flagging as legacy, because the framework still receives occasional upstream cleanup (a hardening patch in 2026 and treewide bus-API maintenance in 2024) yet its only real-world users are devices like the Nokia N900, which today survives mainly through postmarketOS rather than retail sales. There is no removal pressure, but a note marking it as legacy mobile-modem plumbing would help future maintainers.
repository signals
sources
- lore.kernel.org
HSI core still receives upstream attention; a non-mechanical hardening cleanup for hsi_core.c was posted on 2026-03-18.
- lore.kernel.org
HSI core also saw treewide API maintenance in 2024, indicating the code is not abandoned in-tree.
- wiki.postmarketos.org
The remaining visible real-world deployment is niche legacy hardware: postmarketOS still documents Nokia N900 support, with modem calls only partial but SMS/mobile data working.
- en.wikipedia.org
The best-known end-user hardware tied to this stack, the Nokia N900, is a 2009 device; by 2023 it was already described as being kept alive mainly by postmarketOS rather than current retail sales.
codex reasoning notes (technical)
Local shell inspection shows this directory is the HSI bus/framework core, while its only concrete in-tree controller/client bindings are legacy OMAP SSI and Nokia N900 modem support; Kconfig explicitly calls OMAP SSI a legacy HSI variant used to connect an application engine to a cellular modem. lore_file_timeline on drivers/hsi/hsi_core.c produced the 2026 and 2024 lore URLs above, so there is still occasional upstream bug-fix/treewide maintenance and no confirmed removal signal. Web search produced the postmarketOS and Wikipedia URLs, which support 'low' present-day deployment on legacy hobbyist/industrial-ish devices rather than new 2025 sales. Because lore shows ongoing maintenance despite clearly legacy hardware, this fits keep-annotate rather than deprecate/remove.