tile: support new Tilera hypervisor

The Tilera hypervisor shipped in releases up through MDE 4.1 launches
the client operating system (i.e. Linux) at privilege level 1 (PL1).
Starting with MDE 4.2, as part of the work to enable KVM, the
Tilera hypervisor launches Linux at PL2 instead.

This commit makes the KERNEL_PL option default to 2 for tilegx, while
still saying at 1 for tilepro, which doesn't have an updated hypervisor.
It also explains how and when you might want to choose another value.
In addition, we change a small buglet in the on-chip Ethernet driver,
where we were failing to use the KERNEL_PL constant in an API call.

To make the transition cleaner, this change also provides the updated
hv_init() API for the new hypervisor that supports announcing Linux's
compiled-in PL, so the hypervisor can generate a suitable error in the
case of a mismatched hypervisor and Linux binary.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Cc: stable@vger.linux.org

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
index 25877aebc68..41a2a0becc1 100644
--- a/arch/tile/Kconfig
+++ b/arch/tile/Kconfig
@@ -368,11 +368,17 @@ config HARDWALL
 config KERNEL_PL
 	int "Processor protection level for kernel"
 	range 1 2
-	default "1"
+	default 2 if TILEGX
+	default 1 if !TILEGX
 	---help---
-	  This setting determines the processor protection level the
-	  kernel will be built to run at.  Generally you should use
-	  the default value here.
+	  Since MDE 4.2, the Tilera hypervisor runs the kernel
+	  at PL2 by default.  If running under an older hypervisor,
+	  or as a KVM guest, you must run at PL1.  (The current
+	  hypervisor may also be recompiled with "make HV_PL=2" to
+	  allow it to run a kernel at PL1, but clients running at PL1
+	  are not expected to be supported indefinitely.)
+
+	  If you're not sure, don't change the default.
 
 source "arch/tile/gxio/Kconfig"