[RFCv2 4/4] pseries: Advertise HPT resizing support via CAS

[David Gibson <david@gibson.dropbear.id.au>]

The hypervisor needs to know a guest is capable of using the HPT resizing
PAPR extension in order to make full advantage of it for memory hotplug.

If the hypervisor knows the guest is HPT resize aware, it can size the
initial HPT based on the initial guest RAM size, relying on the guest to
resize the HPT when more memory is hot-added.  Without this, the hypervisor
must size the HPT for the maximum possible guest RAM, which can lead to
a huge waste of space if the guest never actually expends to that maximum
size.

This patch advertises the guest's support for HPT resizing via the
ibm,client-architecture-support OF interface.  Obviously, the actual
encoding in the CAS vector is tentative until the extension is officially
incorporated into PAPR.  For now we use bit 0 of (previously unused) byte 8
of option vector 5.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 arch/powerpc/include/asm/prom.h | 1 +
 arch/powerpc/kernel/prom_init.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/prom.h b/arch/powerpc/include/asm/prom.h
index 7f436ba..7a57b77 100644
--- a/arch/powerpc/include/asm/prom.h
+++ b/arch/powerpc/include/asm/prom.h
@@ -151,6 +151,7 @@ struct of_drconf_cell {
 #define OV5_XCMO		0x0440	/* Page Coalescing */
 #define OV5_TYPE1_AFFINITY	0x0580	/* Type 1 NUMA affinity */
 #define OV5_PRRN		0x0540	/* Platform Resource Reassignment */
+#define OV5_HPT_RESIZE		0x880	/* Hash Page Table resizing */
 #define OV5_PFO_HW_RNG		0x0E80	/* PFO Random Number Generator */
 #define OV5_PFO_HW_842		0x0E40	/* PFO Compression Accelerator */
 #define OV5_PFO_HW_ENCR		0x0E20	/* PFO Encryption Accelerator */
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 92dea8d..d82b883 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -712,7 +712,7 @@ unsigned char ibm_architecture_vec[] = {
 	OV5_FEAT(OV5_TYPE1_AFFINITY) | OV5_FEAT(OV5_PRRN),
 	0,
 	0,
-	0,
+	OV5_FEAT(OV5_HPT_RESIZE),
 	/* WARNING: The offset of the "number of cores" field below
 	 * must match by the macro below. Update the definition if
 	 * the structure layout changes.
-- 
2.5.0