platform/x86/amd/hsmp: ACPI HSMP refcounted sockets and coordinated release

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The ACPI driver binds one platform device per socket but shares a single
socket array and a single /dev/hsmp misc device across them. Replace the
is_probed flag with state that tracks this shared ownership:

 - miscdevice.this_device tells whether /dev/hsmp is registered, so the
   misc device is registered on the first socket and torn down last. A
   preceding change clears mdev.this_device on deregister so this gate
   stays reliable across a re-probe.

 - a kref tracks the sockets that share the array. The first probe
   initializes it, each further probe takes a reference and every remove
   (or probe failure) drops one; the last put runs the release callback.
   All get/put happen under hsmp_sock_rwsem held for write, so the counting
   is already serialized and kref's atomic is not strictly needed, but kref
   gives the clearer get/put interface and a release callback. The shared
   socket array is allocated with kcalloc() on the first probe and freed by
   the release callback once the last reference is dropped.

hsmp_acpi_sock_release() is the single teardown helper, run from
kref_put(): it deregisters /dev/hsmp if registered, unmaps any
metric-table DRAM, destroys the per-socket mutexes and frees the array.
The remove path and the probe-failure path both reach it through the last
put, so the teardown lives in one place.

Both paths also clear this socket's dev, so a message issued after a
non-final unbind (or to a socket that failed to probe on a multi-socket
system, whose array stays alive and whose remove() is never called) cannot
reach the mailbox that devres is about to unmap.

Two lifetime fixes fall out of the array persisting across a non-final
unbind:

 - hsmp_get_tbl_dram_base() iounmap()s any stale metric_tbl_addr before
   remapping, so a rebind does not leak one mapping per cycle. It runs
   during (re)probe before the metric sysfs attribute is exposed, so no
   reader can be using the old mapping.

 - The ACPI path registers /dev/hsmp unparented by passing NULL to
   hsmp_misc_register(). Its per-socket devices can be unbound individually
   and out of order and the misc device outlives all but the last of them,
   so parenting it to one socket's device would leave a dangling parent.
   hsmp_misc_register() now takes the parent from its caller, so the
   platform driver keeps parenting /dev/hsmp to its single device.

hsmp_sock_rwsem is held for write across probe and remove, so the release
and probe-failure cleanup run with it already held; an upcoming change adds
its read side so the same lock also drains the data plane.

Signed-off-by: Muralidhara M K <muralidhara.mk@amd.com>
Link: https://patch.msgid.link/20260723094656.3806028-6-muralidhara.mk@amd.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

...

This commit is contained in:

Muralidhara M K 2026-07-23 15:16:55 +05:30 • committed by Ilpo Järvinen

parent 6bd243d5ab

commit 9b2895edb2

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3 changed files with 132 additions and 20 deletions

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131

drivers/platform/x86/amd/hsmp/acpi.c

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20

drivers/platform/x86/amd/hsmp/hsmp.c

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1

drivers/platform/x86/amd/hsmp/hsmp.h

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