Comment 0 for bug 2056373

---Problem Description---
Issues with HVCS and hotplugging issues.

When working on Canonical bug 2023243, it was discovered that mkvterm was not working for multiple reasons. This bug will cover the issues found in HVCS, and hotplugging issues found when drmgr writes the slot information to .../add_slot.

When mkvterm is ran, it ultimately fails because it calls pvmutil which fails. pvmutil calls drmgr, and drmgr is adding a slot correctly. However, when drmgr writes the slot information to ?/add_slot, the return is -ENODEV. This leads to HVCS never having probe() called. In addition, HVCS is missing patches, and is broken without them. 8 kernel patches have been identified to fix these issues.

---uname output---
Linux neop91.pok.stglabs.ibm.com 5.4.0-173-generic #191-Ubuntu SMP Fri Feb 2 13:54:35 UTC 2024 ppc64le ppc64le ppc64le GNU/Linux

---Steps to Reproduce---
 Run mkvterm with an id. mkvterm will fail because /dev/hvcs* device nodes are missing. See https://bugs.launchpad.net/ubuntu/+source/powerpc-utils/+bug/2023243 for more information.

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2 commits made to arch/powerpc/platforms/pseries/of_helpers.c are needed. These commits fix the hotplugging issue seen when drmgr goes to write the slot information to /sys/bus/pci/slots/control/add_slot. This is also why the HVCS device nodes were not being created, as mentioned in the previous bug.

The issue lies in rpadlpar_io and rpaphp calling an of helper function of_read_drc_info_cell(). Without these commits, the value stored drc_index_start is incorrect. This ultimately results in the entire SLOT string being incorrect, and rpaphp never finding the newly added slot by drmgr. rpadlpar then returns -ENODEV. Therefore, HVCS is never probed, and the device nodes are never created.

Ideally - HVCS, rpadlpar_io, and rpaphp should not even need to be loaded prior to drmgr adding a vio slot. If rpadlpar_io and rpaphp are not loaded, drmgr will load them. In addition, if rpadlpar_io and rpaphp register the new slot correctly, rpadlpar_io will call dlpar_add_vio_slot(), which calls vio_register_device_node() with the device node. This is what tells the driver core to init and probe HVCS (which is needed to create the device nodes).

In addition to the 2 commits mentioned above, 6 HVCS commits are needed. HVCS is essentially broken without them. Issues include race conditions, hotplug remove issues, as well as memory leaks. These commits have been added to other distros after multiple issues were seen. Without these commits, 20.04 will experience the same issues. IBM plans on stress testing these changes after an updated kernel is provided in focal-proposed.

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2 commits that make changes to arch/powerpc/platforms/pseries/of_helpers.c:

powerpc/pseries: Fix bad drc_index_start value parsing of drc-info entry
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=57409d4fb12c185b2c0689e0496878c8f6bb5b58

powerpc/pseries: Fix of_read_drc_info_cell() to point at next record
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c5e76fa05b2df519b9f08571cc57e623c1569faa

HVCS commits:

hvcs: Fix hvcs port reference counting
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6a9a733edd46732e906d976dc21a42dd361e53cc

hvcs: Use dev_groups to manage hvcs device attributes
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=760aa5e81f33e0da82512c4288489739a6d1c556

hvcs: Use driver groups to manage driver attributes
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=503a90dd619d52dcac2cc68bd742aa914c7cd47a

hvcs: Get reference to tty in remove
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3a8d3b366ce47024bf274eac783f8af5df2780f5

hvcs: Use vhangup in hotplug remove
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d432228bc7b1b3f0ed06510278ff5a77b3749fe6

hvcs: Synchronize hotplug remove with port free
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=28d49f8cbe9c7966f91ee1b5ec2f997f6e55bf9f