This fixes a bug which if we probe a non-existing
I2C device, and the SMU returns 0xFF, from then on
we can never communicate with the SMU, because the
code before this patch reads and interprets 0xFF
as a terminal error, and thus we never write 0
into register 90 to clear the status (and
subsequently send a new command to the SMU.)

It is not an error that the SMU returns status
0xFF. This means that the SMU executed the last
command successfully (execution status), but the
command result is an error of some sort (execution
result), depending on what the command was.

When doing a status check of the SMU, before we
send a new command, the only status which
precludes us from sending a new command is 0--the
SMU hasn't finished executing a previous command,
and 0xFC--the SMU is busy.

This bug was seen as the following line in the
kernel log,

amdgpu: Msg issuing pre-check failed(0xff) and SMU may be not in the right state!

when subsequent SMU commands, not necessarily
related to I2C, were sent to the SMU.

This patch fixes this bug.

v2: Add a comment to the description of
__smu_cmn_poll_stat() to explain why we're NOT
defining the SMU FW return codes as macros, but
are instead hard-coding them. Such a change, can
be followed up by a subsequent patch.

v3: The changes are,
a) Add comments to break labels in
   __smu_cmn_reg2errno().

b) When an unknown/unspecified/undefined result is
   returned back from the SMU, map that to
   -EREMOTEIO, to distinguish failure at the SMU
   FW.

c) Add kernel-doc to
   smu_cmn_send_msg_without_waiting(),
   smu_cmn_wait_for_response(),
   smu_cmn_send_smc_msg_with_param().

d) In smu_cmn_send_smc_msg_with_param(), since we
   wait for completion of the command, if the
   result of the completion is
   undefined/unknown/unspecified, we print that to
   the kernel log.

v4: a) Add macros as requested, though redundant, to
    be removed when SMU consolidates for all
    ASICs--see comment in code.
    b) Get out if the SMU code is unknown.

v5: Rename the macro names.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Evan Quan <evan.quan@amd.com>
Cc: Lijo Lazar <Lijo.Lazar@amd.com>
Fixes: fcb1fe9c ("drm/amd/powerplay: pre-check the SMU state before issuing message")
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>