When processing a SYSERR, if the device does not respond to the MHI_RESET
from the host, the host will be stuck in a difficult to recover state.
The host will remain in MHI_PM_SYS_ERR_PROCESS and not clean up the host
channels.  Clients will not be notified of the SYSERR via the destruction
of their channel devices, which means clients may think that the device is
still up.  Subsequent SYSERR events such as a device fatal error will not
be processed as the state machine cannot transition from PROCESS back to
DETECT.  The only way to recover from this is to unload the mhi module
(wipe the state machine state) or for the mhi controller to initiate
SHUTDOWN.

This issue was discovered by stress testing soc_reset events on AIC100
via the sysfs node.

soc_reset is processed entirely in hardware.  When the register write
hits the endpoint hardware, it causes the soc to reset without firmware
involvement.  In stress testing, there is a rare race where soc_reset N
will cause the soc to reset and PBL to signal SYSERR (fatal error).  If
soc_reset N+1 is triggered before PBL can process the MHI_RESET from the
host, then the soc will reset again, and re-run PBL from the beginning.
This will cause PBL to lose all state.  PBL will be waiting for the host
to respond to the new syserr, but host will be stuck expecting the
previous MHI_RESET to be processed.

Additionally, the AMSS EE firmware (QSM) was hacked to synthetically
reproduce the issue by simulating a FW hang after the QSM issued a
SYSERR.  In this case, soc_reset would not recover the device.

For this failure case, to recover the device, we need a state similar to
PROCESS, but can transition to DETECT.  There is not a viable existing
state to use.  POR has the needed transitions, but assumes the device is
in a good state and could allow the host to attempt to use the device.
Allowing PROCESS to transition to DETECT invites the possibility of
parallel SYSERR processing which could get the host and device out of
sync.

Thus, invent a new state - MHI_PM_SYS_ERR_FAIL

This essentially a holding state.  It allows us to clean up the host
elements that are based on the old state of the device (channels), but
does not allow us to directly advance back to an operational state.  It
does allow the detection and processing of another SYSERR which may
recover the device, or allows the controller to do a clean shutdown.
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Carl Vanderlip <quic_carlv@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20240112180800.536733-1-quic_jhugo@quicinc.comSigned-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>