arm: Replace v7_maint_dcache_all(ARMV7_DCACHE_CLEAN_INVAL_ALL) with asm code

v7_maint_dcache_all() does not work reliable when build with gcc6,
see: https://bugzilla.redhat.com/show_bug.cgi?id=1318788

While debugging this I learned that v7_maint_dcache_all() is unreliable
when build with gcc5 too when it is marked as noinline.

This commit fixes the reliability issues by replacing the C-code with
the ready to use asm implementation from the kernel.

Given that this code when written as C-code clearly is quite fragile
(also see the existing comments about the C-code being the way it is
 to get optimal assembly) and that we have a proven asm alternative,
I believe that this is the best solution.

Note that we actually already had a copy of the kernel's
v7_flush_dcache_all() before this commit in
arch/arm/mach-uniphier/arm32/lowlevel_init.S.

This commit moves that code arch/arm/cpu/armv7/cache_v7_asm.S, renames
it to __v7_flush_dcache_all(), and adds a v7_flush_dcache_all() wrapper
which saves / restores the clobbered registers for use from C-code.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/cpu/armv7/Makefile

@@ -7,7 +7,7 @@
 
 extra-y	:= start.o
 
-obj-y	+= cache_v7.o
+obj-y	+= cache_v7.o cache_v7_asm.o
 
 obj-y	+= cpu.o cp15.o
 obj-y	+= syslib.o

arch/arm/cpu/armv7/cache_v7.c

@@ -16,6 +16,10 @@
 #define ARMV7_DCACHE_CLEAN_INVAL_RANGE	4
 
 #ifndef CONFIG_SYS_DCACHE_OFF
+
+/* Asm functions from cache_v7_asm.S */
+void v7_flush_dcache_all(void);
+
 static int check_cache_range(unsigned long start, unsigned long stop)
 {
 	int ok = 1;
@@ -88,34 +92,6 @@ static void v7_inval_dcache_level_setway(u32 level, u32 num_sets,
 	DSB;
 }
 
-static void v7_clean_inval_dcache_level_setway(u32 level, u32 num_sets,
-					       u32 num_ways, u32 way_shift,
-					       u32 log2_line_len)
-{
-	int way, set;
-	u32 setway;
-
-	/*
-	 * For optimal assembly code:
-	 *	a. count down
-	 *	b. have bigger loop inside
-	 */
-	for (way = num_ways - 1; way >= 0 ; way--) {
-		for (set = num_sets - 1; set >= 0; set--) {
-			setway = (level << 1) | (set << log2_line_len) |
-				 (way << way_shift);
-			/*
-			 * Clean & Invalidate data/unified
-			 * cache line by set/way
-			 */
-			asm volatile ("	mcr p15, 0, %0, c7, c14, 2"
-					: : "r" (setway));
-		}
-	}
-	/* DSB to make sure the operation is complete */
-	DSB;
-}
-
 static void v7_maint_dcache_level_setway(u32 level, u32 operation)
 {
 	u32 ccsidr;
@@ -142,13 +118,8 @@ static void v7_maint_dcache_level_setway(u32 level, u32 operation)
 	log2_num_ways = log_2_n_round_up(num_ways);
 
 	way_shift = (32 - log2_num_ways);
-	if (operation == ARMV7_DCACHE_INVAL_ALL) {
-		v7_inval_dcache_level_setway(level, num_sets, num_ways,
+	v7_inval_dcache_level_setway(level, num_sets, num_ways,
 				      way_shift, log2_line_len);
-	} else if (operation == ARMV7_DCACHE_CLEAN_INVAL_ALL) {
-		v7_clean_inval_dcache_level_setway(level, num_sets, num_ways,
-						   way_shift, log2_line_len);
-	}
 }
 
 static void v7_maint_dcache_all(u32 operation)
@@ -263,7 +234,7 @@ void invalidate_dcache_all(void)
  */
 void flush_dcache_all(void)
 {
-	v7_maint_dcache_all(ARMV7_DCACHE_CLEAN_INVAL_ALL);
+	v7_flush_dcache_all();
 
 	v7_outer_cache_flush_all();
 }

arch/arm/cpu/armv7/cache_v7_asm.S

@@ -0,0 +1,84 @@
+/*
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <config.h>
+#include <linux/linkage.h>
+#include <linux/sizes.h>
+#include <asm/system.h>
+
+#ifdef CONFIG_SYS_THUMB_BUILD
+#define ARM(x...)
+#define THUMB(x...)	x
+#else
+#define ARM(x...)	x
+#define THUMB(x...)
+#endif
+
+/*
+ *	v7_flush_dcache_all()
+ *
+ *	Flush the whole D-cache.
+ *
+ *	Corrupted registers: r0-r7, r9-r11 (r6 only in Thumb mode)
+ *
+ *	Note: copied from arch/arm/mm/cache-v7.S of Linux 4.4
+ */
+ENTRY(__v7_flush_dcache_all)
+	dmb					@ ensure ordering with previous memory accesses
+	mrc	p15, 1, r0, c0, c0, 1		@ read clidr
+	mov	r3, r0, lsr #23			@ move LoC into position
+	ands	r3, r3, #7 << 1			@ extract LoC*2 from clidr
+	beq	finished			@ if loc is 0, then no need to clean
+start_flush_levels:
+	mov	r10, #0				@ start clean at cache level 0
+flush_levels:
+	add	r2, r10, r10, lsr #1		@ work out 3x current cache level
+	mov	r1, r0, lsr r2			@ extract cache type bits from clidr
+	and	r1, r1, #7			@ mask of the bits for current cache only
+	cmp	r1, #2				@ see what cache we have at this level
+	blt	skip				@ skip if no cache, or just i-cache
+	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
+	isb					@ isb to sych the new cssr&csidr
+	mrc	p15, 1, r1, c0, c0, 0		@ read the new csidr
+	and	r2, r1, #7			@ extract the length of the cache lines
+	add	r2, r2, #4			@ add 4 (line length offset)
+	movw	r4, #0x3ff
+	ands	r4, r4, r1, lsr #3		@ find maximum number on the way size
+	clz	r5, r4				@ find bit position of way size increment
+	movw	r7, #0x7fff
+	ands	r7, r7, r1, lsr #13		@ extract max number of the index size
+loop1:
+	mov	r9, r7				@ create working copy of max index
+loop2:
+ ARM(	orr	r11, r10, r4, lsl r5	)	@ factor way and cache number into r11
+ THUMB(	lsl	r6, r4, r5		)
+ THUMB(	orr	r11, r10, r6		)	@ factor way and cache number into r11
+ ARM(	orr	r11, r11, r9, lsl r2	)	@ factor index number into r11
+ THUMB(	lsl	r6, r9, r2		)
+ THUMB(	orr	r11, r11, r6		)	@ factor index number into r11
+	mcr	p15, 0, r11, c7, c14, 2		@ clean & invalidate by set/way
+	subs	r9, r9, #1			@ decrement the index
+	bge	loop2
+	subs	r4, r4, #1			@ decrement the way
+	bge	loop1
+skip:
+	add	r10, r10, #2			@ increment cache number
+	cmp	r3, r10
+	bgt	flush_levels
+finished:
+	mov	r10, #0				@ swith back to cache level 0
+	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
+	dsb	st
+	isb
+	bx	lr
+ENDPROC(__v7_flush_dcache_all)
+
+ENTRY(v7_flush_dcache_all)
+ ARM(	stmfd	sp!, {r4-r5, r7, r9-r11, lr}	)
+ THUMB(	stmfd	sp!, {r4-r7, r9-r11, lr}	)
+	bl	__v7_flush_dcache_all
+ ARM(	ldmfd	sp!, {r4-r5, r7, r9-r11, lr}	)
+ THUMB(	ldmfd	sp!, {r4-r7, r9-r11, lr}	)
+	bx	lr
+ENDPROC(v7_flush_dcache_all)

arch/arm/mach-uniphier/arm32/lowlevel_init.S

@@ -38,7 +38,7 @@ ENTRY(lowlevel_init)
 	 * to do next is to create a page table and switch over to it.
 	 */
 	bl	create_page_table
-	bl	v7_flush_dcache_all
+	bl	__v7_flush_dcache_all
 
 	/* Disable MMU and Dcache before switching Page Table */
 	mrc	p15, 0, r0, c1, c0, 0	@ SCTLR (System Control Register)
@@ -140,68 +140,3 @@ ENTRY(create_page_table)
 	str	r0, [r12, #4]		@ mark the second section as Normal
 	mov	pc, lr
 ENDPROC(create_page_table)
-
-/* We don't use Thumb instructions for now */
-#define ARM(x...)	x
-#define THUMB(x...)
-
-/*
- *	v7_flush_dcache_all()
- *
- *	Flush the whole D-cache.
- *
- *	Corrupted registers: r0-r7, r9-r11 (r6 only in Thumb mode)
- *
- *	- mm    - mm_struct describing address space
- *
- *	Note: copied from arch/arm/mm/cache-v7.S of Linux 4.4
- */
-ENTRY(v7_flush_dcache_all)
-	dmb					@ ensure ordering with previous memory accesses
-	mrc	p15, 1, r0, c0, c0, 1		@ read clidr
-	mov	r3, r0, lsr #23			@ move LoC into position
-	ands	r3, r3, #7 << 1			@ extract LoC*2 from clidr
-	beq	finished			@ if loc is 0, then no need to clean
-start_flush_levels:
-	mov	r10, #0				@ start clean at cache level 0
-flush_levels:
-	add	r2, r10, r10, lsr #1		@ work out 3x current cache level
-	mov	r1, r0, lsr r2			@ extract cache type bits from clidr
-	and	r1, r1, #7			@ mask of the bits for current cache only
-	cmp	r1, #2				@ see what cache we have at this level
-	blt	skip				@ skip if no cache, or just i-cache
-	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
-	isb					@ isb to sych the new cssr&csidr
-	mrc	p15, 1, r1, c0, c0, 0		@ read the new csidr
-	and	r2, r1, #7			@ extract the length of the cache lines
-	add	r2, r2, #4			@ add 4 (line length offset)
-	movw	r4, #0x3ff
-	ands	r4, r4, r1, lsr #3		@ find maximum number on the way size
-	clz	r5, r4				@ find bit position of way size increment
-	movw	r7, #0x7fff
-	ands	r7, r7, r1, lsr #13		@ extract max number of the index size
-loop1:
-	mov	r9, r7				@ create working copy of max index
-loop2:
- ARM(	orr	r11, r10, r4, lsl r5	)	@ factor way and cache number into r11
- THUMB(	lsl	r6, r4, r5		)
- THUMB(	orr	r11, r10, r6		)	@ factor way and cache number into r11
- ARM(	orr	r11, r11, r9, lsl r2	)	@ factor index number into r11
- THUMB(	lsl	r6, r9, r2		)
- THUMB(	orr	r11, r11, r6		)	@ factor index number into r11
-	mcr	p15, 0, r11, c7, c14, 2		@ clean & invalidate by set/way
-	subs	r9, r9, #1			@ decrement the index
-	bge	loop2
-	subs	r4, r4, #1			@ decrement the way
-	bge	loop1
-skip:
-	add	r10, r10, #2			@ increment cache number
-	cmp	r3, r10
-	bgt	flush_levels
-finished:
-	mov	r10, #0				@ swith back to cache level 0
-	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
-	dsb	st
-	isb
-	mov	pc, lr
-ENDPROC(v7_flush_dcache_all)