[PATCH v3 0/4] platform/x86: intel_scu_ipc: Timeout fixes

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I recently looked at some crash reports on ChromeOS devices that call
into this intel_scu_ipc driver. They were hitting timeouts, and it
certainly looks possible for those timeouts to be triggering because of
scheduling issues. Once things started going south, the timeouts kept
coming. Maybe that's because the other side got seriously confused? I
don't know.

I added some sleeps to these paths to trigger the timeout behavior to
make sure the code works. Simply sleeping for a long time in busy_loop()
hits the timeout, which could happen if the system is scheduling lots of
other things at the time.

I couldn't really test the third patch because forcing a timeout or
returning immediately wasn't fast enough to trigger the second
transaction to run into the first one being processed.

Changes from v2 (https://lore.kernel.org/r/20230906180944.2197111-1-swboyd@xxxxxxxxxxxx):
 * Use read_poll_timeout() helper in patch #1 (again)
 * New patch #3 to fix bug pointed out by Andy
 * Consolidate more code into busy check in patch #4

Changes from v1 (https://lore.kernel.org/r/20230831011405.3246849-1-swboyd@xxxxxxxxxxxx):
 * Don't use read_poll_timeout() helper in patch 1, just add code
 * Rewrite patch 2 to be simpler
 * Make intel_scu_ipc_busy() return -EBUSY when busy
 * Downgrade dev_err() to dev_dbg() in intel_scu_ipc_busy()

Stephen Boyd (4):
  platform/x86: intel_scu_ipc: Check status after timeout in busy_loop()
  platform/x86: intel_scu_ipc: Check status upon timeout in
  platform/x86: intel_scu_ipc: Don't override scu in
  platform/x86: intel_scu_ipc: Fail IPC send if still busy

 drivers/platform/x86/intel_scu_ipc.c | 66 +++++++++++++++++-----------
 1 file changed, 40 insertions(+), 26 deletions(-)

Cc: Prashant Malani <pmalani@xxxxxxxxxxxx>

base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c

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