powerpc/powernv: Add explicit fast-reboot support

Add a way to manually invoke a fast-reboot rather than setting the NVRAM
flag. The idea is to allow userspace to invoke a fast-reboot using the
optional string argument to the reboot() system call, or using the xmon
zr command so we don't need to leave around a persistent changes on
a system to use the feature.
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200217024833.30580-2-oohall@gmail.com

arch/powerpc/include/asm/opal-api.h

@@ -1067,6 +1067,7 @@ enum {
 	OPAL_REBOOT_PLATFORM_ERROR	= 1,
 	OPAL_REBOOT_FULL_IPL		= 2,
 	OPAL_REBOOT_MPIPL		= 3,
+	OPAL_REBOOT_FAST		= 4,
 };
 
 /* Argument to OPAL_PCI_TCE_KILL */

arch/powerpc/platforms/powernv/setup.c

@@ -237,6 +237,8 @@ static void  __noreturn pnv_restart(char *cmd)
 			rc = opal_cec_reboot2(OPAL_REBOOT_MPIPL, NULL);
 		else if (strcmp(cmd, "error") == 0)
 			rc = opal_cec_reboot2(OPAL_REBOOT_PLATFORM_ERROR, NULL);
+		else if (strcmp(cmd, "fast") == 0)
+			rc = opal_cec_reboot2(OPAL_REBOOT_FAST, NULL);
 		else
 			rc = OPAL_UNSUPPORTED;