We don't implement separate flush_dcache_all intentionally as entire data cache invalidation is dangerous operation even if we flush data cache right before invalidation.
There is the real example: We may hang in the next code if we store any context (like BLINK register) on stack in invalidate_dcache_all() function. BLINK register is the register where return address is automatically saved when we do function call with instructions like 'bl'.
void flush_dcache_all() { __dc_entire_op(OP_FLUSH); // Other code // }
void invalidate_dcache_all() { __dc_entire_op(OP_INV); // Other code // }
void foo(void) { flush_dcache_all(); invalidate_dcache_all(); }
Now let's see what really happens during that code execution:
foo() |->> call flush_dcache_all [return address is saved to BLINK register] [push BLINK] (save to stack) ![point 1] |->> call __dc_entire_op(OP_FLUSH) [return address is saved to BLINK register] [flush L1 D$] return [jump to BLINK] <<------ [other flush_dcache_all code] [pop BLINK] (get from stack) return [jump to BLINK] <<------ |->> call invalidate_dcache_all [return address is saved to BLINK register] [push BLINK] (save to stack) ![point 2] |->> call __dc_entire_op(OP_FLUSH) [return address is saved to BLINK register] [invalidate L1 D$] ![point 3] // Oops!!! // We lose return address from invalidate_dcache_all function: // we save it to stack and invalidate L1 D$ after that! return [jump to BLINK] <<------ [other invalidate_dcache_all code] [pop BLINK] (get from stack) // we don't have this data in L1 dcache as we invalidated it in [point 3] // so we get it from next memory level (for example DDR memory) // but in the memory we have value which we save in [point 1], which // is return address from flush_dcache_all function (instead of // address from current invalidate_dcache_all function which we // saved in [point 2] !) return [jump to BLINK] <<------ // As BLINK points to invalidate_dcache_all, we call it again and // loop forever.
Fortunately we may do flush and invalidation of D$ with a single one instruction which automatically mitigates a situation described above.
And because invalidate_dcache_all isn't used in common u-boot code we implement "flush and invalidate dcache all" instead.
Signed-off-by: Eugeniy Paltsev Eugeniy.Paltsev@synopsys.com --- arch/arc/include/asm/cache.h | 1 + arch/arc/lib/cache.c | 89 +++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 85 insertions(+), 5 deletions(-)
diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h index d26d9fb18d..382c4126c3 100644 --- a/arch/arc/include/asm/cache.h +++ b/arch/arc/include/asm/cache.h @@ -30,6 +30,7 @@ #ifndef __ASSEMBLY__
void cache_init(void); +void flush_n_invalidate_dcache_all(void);
#endif /* __ASSEMBLY__ */
diff --git a/arch/arc/lib/cache.c b/arch/arc/lib/cache.c index 83b77b9716..42207b201c 100644 --- a/arch/arc/lib/cache.c +++ b/arch/arc/lib/cache.c @@ -12,6 +12,80 @@ #include <asm/arcregs.h> #include <asm/cache.h>
+/* + * [ NOTE 1 ]: + * Data cache (L1 D$ or SL$) entire invalidate operation or data cache disable + * operation may result in unexpected behavior and data loss even if we flush + * data cache right before invalidation. That may happens if we store any context + * on stack (like we store BLINK register on stack before function call). + * BLINK register is the register where return address is automatically saved + * when we do function call with instructions like 'bl'. + * + * There is the real example: + * We may hang in the next code as we store any BLINK register on stack in + * invalidate_dcache_all() function. + * + * void flush_dcache_all() { + * __dc_entire_op(OP_FLUSH); + * // Other code // + * } + * + * void invalidate_dcache_all() { + * __dc_entire_op(OP_INV); + * // Other code // + * } + * + * void foo(void) { + * flush_dcache_all(); + * invalidate_dcache_all(); + * } + * + * Now let's see what really happens during that code execution: + * + * foo() + * |->> call flush_dcache_all + * [return address is saved to BLINK register] + * [push BLINK] (save to stack) ![point 1] + * |->> call __dc_entire_op(OP_FLUSH) + * [return address is saved to BLINK register] + * [flush L1 D$] + * return [jump to BLINK] + * <<------ + * [other flush_dcache_all code] + * [pop BLINK] (get from stack) + * return [jump to BLINK] + * <<------ + * |->> call invalidate_dcache_all + * [return address is saved to BLINK register] + * [push BLINK] (save to stack) ![point 2] + * |->> call __dc_entire_op(OP_FLUSH) + * [return address is saved to BLINK register] + * [invalidate L1 D$] ![point 3] + * // Oops!!! + * // We lose return address from invalidate_dcache_all function: + * // we save it to stack and invalidate L1 D$ after that! + * return [jump to BLINK] + * <<------ + * [other invalidate_dcache_all code] + * [pop BLINK] (get from stack) + * // we don't have this data in L1 dcache as we invalidated it in [point 3] + * // so we get it from next memory level (for example DDR memory) + * // but in the memory we have value which we save in [point 1], which + * // is return address from flush_dcache_all function (instead of + * // address from current invalidate_dcache_all function which we + * // saved in [point 2] !) + * return [jump to BLINK] + * <<------ + * // As BLINK points to invalidate_dcache_all, we call it again and + * // loop forever. + * + * Fortunately we may fix that by using flush & invalidation of D$ with a single + * one instruction (instead of flush and invalidation instructions pair) and + * enabling force function inline with '__attribute__((always_inline))' gcc + * attribute to avoid any function call (and BLINK store) between cache flush + * and disable. + */ + /* Bit values in IC_CTRL */ #define IC_CTRL_CACHE_DISABLE BIT(0)
@@ -256,8 +330,7 @@ void cache_init(void) /* IOC Aperture size is equal to DDR size */ long ap_size = CONFIG_SYS_SDRAM_SIZE;
- flush_dcache_all(); - invalidate_dcache_all(); + flush_n_invalidate_dcache_all();
if (!is_power_of_2(ap_size) || ap_size < 4096) panic("IOC Aperture size must be power of 2 and bigger 4Kib"); @@ -483,13 +556,19 @@ void flush_cache(unsigned long start, unsigned long size) flush_dcache_range(start, start + size); }
-void invalidate_dcache_all(void) +/* + * As invalidate_dcache_all() is not used in generic U-Boot code and as we + * don't need it in arch/arc code alone (invalidate without flush) we implement + * flush_n_invalidate_dcache_all (flush and invalidate in 1 operation) because + * it's much safer. See [ NOTE 1 ] for more details. + */ +void flush_n_invalidate_dcache_all(void) { - __dc_entire_op(OP_INV); + __dc_entire_op(OP_FLUSH_N_INV);
#ifdef CONFIG_ISA_ARCV2 if (slc_exists) - __slc_entire_op(OP_INV); + __slc_entire_op(OP_FLUSH_N_INV); #endif }