powerpc/pseries: Set CPU_FTR_DBELL according to ibm,pi-features

PAPR will define a new ibm,pi-features bit which says that doorbells
should not be used even on architectures where they exist. This could be
because they are emulated and slower than using the interrupt controller
directly for IPIs.

Wire this bit into the pi-features parser to clear CPU_FTR_DBELL, and
ensure CPU_FTR_DBELL is not in CPU_FTRS_ALWAYS.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240207035220.339726-2-npiggin@gmail.com

arch/powerpc/include/asm/cputable.h

@@ -545,19 +545,20 @@ enum {
 #define CPU_FTRS_DT_CPU_BASE	(~0ul)
 #endif
 
+/* pseries may disable DBELL with ibm,pi-features */
 #ifdef CONFIG_CPU_LITTLE_ENDIAN
 #define CPU_FTRS_ALWAYS \
-	    (CPU_FTRS_POSSIBLE & ~CPU_FTR_HVMODE & CPU_FTRS_POWER7 & \
-	     CPU_FTRS_POWER8E & CPU_FTRS_POWER8 & CPU_FTRS_POWER9 & \
-	     CPU_FTRS_POWER9_DD2_1 & CPU_FTRS_POWER9_DD2_2 & \
+	    (CPU_FTRS_POSSIBLE & ~CPU_FTR_HVMODE & ~CPU_FTR_DBELL & \
+	     CPU_FTRS_POWER7 & CPU_FTRS_POWER8E & CPU_FTRS_POWER8 & \
+	     CPU_FTRS_POWER9 & CPU_FTRS_POWER9_DD2_1 & CPU_FTRS_POWER9_DD2_2 & \
 	     CPU_FTRS_POWER10 & CPU_FTRS_DT_CPU_BASE)
 #else
 #define CPU_FTRS_ALWAYS		\
 	    (CPU_FTRS_PPC970 & CPU_FTRS_POWER5 & \
 	     CPU_FTRS_POWER6 & CPU_FTRS_POWER7 & CPU_FTRS_CELL & \
 	     CPU_FTRS_PA6T & CPU_FTRS_POWER8 & CPU_FTRS_POWER8E & \
-	     ~CPU_FTR_HVMODE & CPU_FTRS_POSSIBLE & CPU_FTRS_POWER9 & \
-	     CPU_FTRS_POWER9_DD2_1 & CPU_FTRS_POWER9_DD2_2 & \
+	     ~CPU_FTR_HVMODE & ~CPU_FTR_DBELL & CPU_FTRS_POSSIBLE & \
+	     CPU_FTRS_POWER9 & CPU_FTRS_POWER9_DD2_1 & CPU_FTRS_POWER9_DD2_2 & \
 	     CPU_FTRS_POWER10 & CPU_FTRS_DT_CPU_BASE)
 #endif /* CONFIG_CPU_LITTLE_ENDIAN */
 #endif

arch/powerpc/kernel/prom.c

@@ -196,6 +196,7 @@ static struct ibm_feature ibm_pa_features[] __initdata = {
  */
 static struct ibm_feature ibm_pi_features[] __initdata = {
 	{ .pabyte = 0, .pabit = 3, .mmu_features  = MMU_FTR_NX_DSI },
+	{ .pabyte = 0, .pabit = 4, .cpu_features  = CPU_FTR_DBELL, .clear = 1 },
 };
 
 static void __init scan_features(unsigned long node, const unsigned char *ftrs,