generic: MIPS: Add barriers between dcache & icache flushes

This fixes spurious boot-errors with some ath79 MIPS 74Kc boards such
as the AC Lite as well as Archer C7 v2.

The missing barrier leads to the icache flush being executed before the
dcache writeback, which results in the CPU executing the dummy infinite
loop in tlbmiss_handler_setup_pgd.

Applying this patch from upstream ensures the dcache is written back
before flushing the icache.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/generic/pending-5.10/301-MIPS-Add-barriers-between-dcache-icache-flushes.patch

@@ -0,0 +1,71 @@
+From e6e6ef4275978823ec3a84133fc91f4ffbef5c84 Mon Sep 17 00:00:00 2001
+From: Paul Burton <paul.burton@imgtec.com>
+Date: Mon, 22 Feb 2016 18:09:44 +0000
+Subject: [PATCH] MIPS: Add barriers between dcache & icache flushes
+
+Index-based cache operations may be arbitrarily reordered by out of
+order CPUs. Thus code which writes back the dcache & then invalidates
+the icache using indexed cache ops must include a barrier between
+operating on the 2 caches in order to prevent the scenario in which:
+
+  - icache invalidation occurs.
+
+  - icache fetch occurs, due to speculation.
+
+  - dcache writeback occurs.
+
+If the above were allowed to happen then the icache would contain stale
+data. Forcing the dcache writeback to complete before the icache
+invalidation avoids this.
+
+Signed-off-by: Paul Burton <paul.burton@imgtec.com>
+Cc: James Hogan <james.hogan@imgtec.com>
+---
+ arch/mips/mm/c-r4k.c | 13 +++++++++++--
+ 1 file changed, 11 insertions(+), 2 deletions(-)
+
+--- a/arch/mips/mm/c-r4k.c
++++ b/arch/mips/mm/c-r4k.c
+@@ -515,6 +515,7 @@ static inline void local_r4k___flush_cac
+
+ 	default:
+ 		r4k_blast_dcache();
++		mb(); /* cache instructions may be reordered */
+ 		r4k_blast_icache();
+ 		break;
+ 	}
+@@ -595,8 +596,10 @@ static inline void local_r4k_flush_cache
+ 	if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc))
+ 		r4k_blast_dcache();
+ 	/* If executable, blast stale lines from icache */
+-	if (exec)
++	if (exec) {
++		mb(); /* cache instructions may be reordered */
+ 		r4k_blast_icache();
++	}
+ }
+
+ static void r4k_flush_cache_range(struct vm_area_struct *vma,
+@@ -697,8 +700,13 @@ static inline void local_r4k_flush_cache
+ 	if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc)) {
+ 		vaddr ? r4k_blast_dcache_page(addr) :
+ 			r4k_blast_dcache_user_page(addr);
+-		if (exec && !cpu_icache_snoops_remote_store)
++		if (exec)
++			mb(); /* cache instructions may be reordered */
++
++		if (exec && !cpu_icache_snoops_remote_store) {
+ 			r4k_blast_scache_page(addr);
++			mb(); /* cache instructions may be reordered */
++		}
+ 	}
+ 	if (exec) {
+ 		if (vaddr && cpu_has_vtag_icache && mm == current->active_mm) {
+@@ -765,6 +773,7 @@ static inline void __local_r4k_flush_ica
+ 			else
+ 				blast_dcache_range(start, end);
+ 		}
++		mb(); /* cache instructions may be reordered */
+ 	}
+
+ 	if (type == R4K_INDEX ||

target/linux/generic/pending-5.15/301-MIPS-Add-barriers-between-dcache-icache-flushes.patch

@@ -0,0 +1,71 @@
+From e6e6ef4275978823ec3a84133fc91f4ffbef5c84 Mon Sep 17 00:00:00 2001
+From: Paul Burton <paul.burton@imgtec.com>
+Date: Mon, 22 Feb 2016 18:09:44 +0000
+Subject: [PATCH] MIPS: Add barriers between dcache & icache flushes
+
+Index-based cache operations may be arbitrarily reordered by out of
+order CPUs. Thus code which writes back the dcache & then invalidates
+the icache using indexed cache ops must include a barrier between
+operating on the 2 caches in order to prevent the scenario in which:
+
+  - icache invalidation occurs.
+
+  - icache fetch occurs, due to speculation.
+
+  - dcache writeback occurs.
+
+If the above were allowed to happen then the icache would contain stale
+data. Forcing the dcache writeback to complete before the icache
+invalidation avoids this.
+
+Signed-off-by: Paul Burton <paul.burton@imgtec.com>
+Cc: James Hogan <james.hogan@imgtec.com>
+---
+ arch/mips/mm/c-r4k.c | 13 +++++++++++--
+ 1 file changed, 11 insertions(+), 2 deletions(-)
+
+--- a/arch/mips/mm/c-r4k.c
++++ b/arch/mips/mm/c-r4k.c
+@@ -515,6 +515,7 @@ static inline void local_r4k___flush_cac
+
+ 	default:
+ 		r4k_blast_dcache();
++		mb(); /* cache instructions may be reordered */
+ 		r4k_blast_icache();
+ 		break;
+ 	}
+@@ -595,8 +596,10 @@ static inline void local_r4k_flush_cache
+ 	if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc))
+ 		r4k_blast_dcache();
+ 	/* If executable, blast stale lines from icache */
+-	if (exec)
++	if (exec) {
++		mb(); /* cache instructions may be reordered */
+ 		r4k_blast_icache();
++	}
+ }
+
+ static void r4k_flush_cache_range(struct vm_area_struct *vma,
+@@ -697,8 +700,13 @@ static inline void local_r4k_flush_cache
+ 	if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc)) {
+ 		vaddr ? r4k_blast_dcache_page(addr) :
+ 			r4k_blast_dcache_user_page(addr);
+-		if (exec && !cpu_icache_snoops_remote_store)
++		if (exec)
++			mb(); /* cache instructions may be reordered */
++
++		if (exec && !cpu_icache_snoops_remote_store) {
+ 			r4k_blast_scache_page(addr);
++			mb(); /* cache instructions may be reordered */
++		}
+ 	}
+ 	if (exec) {
+ 		if (vaddr && cpu_has_vtag_icache && mm == current->active_mm) {
+@@ -765,6 +773,7 @@ static inline void __local_r4k_flush_ica
+ 			else
+ 				blast_dcache_range(start, end);
+ 		}
++		mb(); /* cache instructions may be reordered */
+ 	}
+
+ 	if (type == R4K_INDEX ||