Add a tunable "hw.mfi.mrsas_enable" to allow mfi(4) to drop priority and

allow mrsas(4) from LSI to attach to newer LSI cards that are support by
mrsas(4).  If mrsas(4) is not loaded into the system at boot then mfi(4)
will always attach.  If a modified mrsas(4) is loaded in the system.  That
modification is return "-30" in it's probe since that is between
BUS_PROBE_DEFAULT and BUS_PROBE_LOW_PRIORITY.

This option is controller by a new probe flag "MFI_FLAGS_MRSAS" in mfi_ident
that denotes cards that should work with mrsas(4).  New entries that should
have this option.

This is the first step to get mrsas(4) checked into FreeBSD and to avoid
collision with people that use mrsas(4) from LSI.  Since mfi(4) takes
priority, then mrsas(4) users need to rebuild GENERIC.  Using the
.disabled="1" method doesn't work since that blocks attaching and the
probe gave it to mfi(4).

Discussed with:		LSI (Kashyap Desai)

1 files changed, 11 insertions, 0 deletions

diff --git a/share/man/man4/mfi.4 b/share/man/man4/mfi.4
index 14dab80..a6d6278 100644
--- a/share/man/man4/mfi.4
+++ b/share/man/man4/mfi.4
@@ -72,6 +72,17 @@ If the sysctl
 .Va dev.mfi.%d.delete_busy_volumes
 is set to 1,
 then the driver will allow mounted volumes to be removed.
+.Pp
+A tunable is provided to adjust the
+.Nm
+driver's behaviour when attaching to a card.  By default the driver will
+attach to all known cards with high probe priority.  If the tunable
+.Va hw.mfi.mrsas_enable
+is set to 1,
+then the driver will reduce its probe priority to allow
+.Cd mrsas
+to attach to the card instead of
+.Nm .
 .Sh HARDWARE
 The
 .Nm