On 4/23/19 7:18 PM, Ahmad Fatoum wrote:
> The ARM Cortex-A Series Programmer's Guide notes[1]:
>> Some care is required with cache maintenance activity in multi-core
Unfortunately, the only error scenario I could find in the ARM docs
was this one here, which presumes a multi-core system.
Lucas, do you have a better example in context of barebox on how things
could go awry without this patch?
>> systems that include a L2C-310 L2 cache (or similar). Cleaning or
>> invalidating the L1 cache and L2 cache will not be a single atomic
>> operation. A core might therefore perform cache maintenance on
>> a particular address in both L1 and L2 caches only as two discrete
>> steps. If another core were to access the affected address between
>> those two actions, a coherency problem can occur. Such problems can
>> be avoided by following two simple rules.
>>
>> * When cleaning, always clean the innermost (L1) cache first and then
>> clean the outer cache(s).
>> * When invalidating, always invalidate the outermost cache first and
>> the L1 cache last.
>
> The current code correctly iterates from inner to outer cache levels
> when flushing/cleaning (r8 == 0), invalidation (r8 == 1) occurs in the
> same direction though. Adjust the invalidation iteration order to start
> from the outermost cache instead.
>
> Equivalent C-Code:
>
> enum cache_op { CACHE_FLUSH = 0, CACHE_INVAL = 1 };
> register enum cache_op operation asm("r8");
> register int i asm("r12");
> register int limit asm("r3") = max_cache_level << 1; // e.g. 4 with L2
> max
>
> +if (operation == CACHE_FLUSH) {
> i = 0;
> +} else {
> + i = limit - 2;
> +}
>
> bool loop_again;
> do {
> /* [snip] */
> + if (operation == CACHE_FLUSH) {
> i += 2;
> loop_again = limit > i;
> + } else {
> + loop_again = i > 0;
> + i -= 2;
> + }
> } while (loop_again);
>
> [1]: 18.6 "TLB and cache maintenance broadcast", Version 4.0
>
> Suggested-by: Lucas Stach <[email protected]>
> Signed-off-by: Ahmad Fatoum <[email protected]>
> ---
> arch/arm/cpu/cache-armv7.S | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/cpu/cache-armv7.S b/arch/arm/cpu/cache-armv7.S
> index 0eb0ecfee756..b2d70bece7b9 100644
> --- a/arch/arm/cpu/cache-armv7.S
> +++ b/arch/arm/cpu/cache-armv7.S
> @@ -83,7 +83,10 @@ hierarchical:
> ands r3, r0, #0x7000000 @ extract loc from clidr
> mov r3, r3, lsr #23 @ left align loc bit field
> beq finished @ if loc is 0, then no need to
> clean
> - mov r12, #0 @ start clean at cache level 0
> + cmp r8, #0
> +THUMB( ite eq )
> + moveq r12, #0
> + subne r12, r3, #2 @ start invalidate at outmost
> cache level
> loop1:
> add r2, r12, r12, lsr #1 @ work out 3x current cache
> level
> mov r1, r0, lsr r2 @ extract cache type bits from
> clidr
> @@ -118,8 +121,15 @@ THUMB( ite eq )
> subs r7, r7, #1 @ decrement the index
> bge loop2
> skip:
> + cmp r8, #0
> + bne inval_check
> add r12, r12, #2 @ increment cache number
> cmp r3, r12
> + b loop_end_check
> +inval_check:
> + cmp r12, #0
> + sub r12, r12, #2 @ decrement cache number
> +loop_end_check:
> #ifdef CONFIG_ARM_ERRATA_814220
> dsb
> #endif
>
--
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