linux-drivers/
drivers/s390/cio

IBM Z and LinuxONE Channel I/O Subsystem (CIO)

The channel I/O subsystem is the low-level glue that lets Linux talk to devices on IBM Z mainframes and LinuxONE servers using the platform's CCW and QDIO channel protocols instead of PC-style buses. It underpins how disks, tape, networking, and crypto hardware are discovered and driven on every Linux instance running on an IBM mainframe, from 1990s S/390 boxes through today's LinuxONE 5.

keep conf=0.96 deploy=medium replacement=none subsystem=s390 category=platform-vendor
96%

recommendation

It should stay because this is the core I/O plumbing for IBM mainframes running Linux, and the hardware family is still being sold new in 2025 — IBM's LinuxONE Emperor 5 reached general availability in June 2025. IBM engineers continue to send fixes upstream (a subchannel cleanup patch landed as recently as October 2025), and there is no replacement because this code is the platform itself.

repository signals

59 files
23,832 source lines
228 commits, 5y
+2,668 / −2,672 lines added / removed, 5y
45 authors, 5y
monthly commits · 2021-04-21 → 2026-04-21 · 228 total · active in 55/61 months
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sources

  1. lore.kernel.org

    Recent non-treewide maintenance continued in 2025 for drivers/s390/cio (example: "s390/cio: Update purge function to unregister the unused subchannels").

  2. ibm.com

    IBM LinuxONE Emperor 5 (9175-ML1) shows General Availability on 2025-06-18, indicating this hardware family was sold new in 2025.

  3. ibm.com

    IBM markets LinuxONE 5 as a current enterprise platform for Linux workloads, supporting the conclusion that new deployments still exist.

codex reasoning notes (technical)

Keep: this is active platform support code for current IBM Z/LinuxONE systems, not a legacy orphan. `lore_activity` on drivers/s390/cio/device.c returned recent 2025 fixes/backports with IBM maintainers, so upstream attention is ongoing. Web search returned IBM lifecycle/product pages showing LinuxONE 5 / Emperor 5 current and GA in 2025, which means the underlying s390 channel-I/O hardware stack remains commercially live. No natural replacement driver exists because this directory is the core I/O subsystem for the platform. URLs obtained via `lore_activity` and `web.search_query` results.