During initialization the driver issues a reset command via its command
interface in order to remove previous configuration from the device.

After issuing the reset, the driver waits for 200ms before polling on
the "system_status" register using memory-mapped IO until the device
reaches a ready state (0x5E). The wait is necessary because the reset
command only triggers the reset, but the reset itself happens
asynchronously. If the driver starts polling too soon, the read of the
"system_status" register will never return and the system will crash
[1].

The issue was discovered when the device was flashed with a development
firmware version where the reset routine took longer to complete. The
issue was fixed in the firmware, but it exposed the fact that the
current wait time is borderline.

Fix by increasing the wait time from 200ms to 400ms. With this patch and
the buggy firmware version, the issue did not reproduce in 10 reboots
whereas without the patch the issue is reproduced quite consistently.

[1]
mce: CPUs not responding to MCE broadcast (may include false positives): 0,4
mce: CPUs not responding to MCE broadcast (may include false positives): 0,4
Kernel panic - not syncing: Timeout: Not all CPUs entered broadcast exception handler
Shutting down cpus with NMI
Kernel Offset: 0x12000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Fixes: ac004e84 ("mlxsw: pci: Wait longer before accessing the device after reset")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>