ARC: Flush & invalidate D$ with a single command
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 get stuck in the following 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>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h
index d26d9fb..382c412 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__ */