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Subject[PATCH 4/4] ARC: IOC: panic if both IOC and ZONE_HIGHMEM enabled
Date
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
---
arch/arc/mm/cache.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
index 34935ce38631..e0b3484641c3 100644
--- a/arch/arc/mm/cache.c
+++ b/arch/arc/mm/cache.c
@@ -1143,6 +1143,19 @@ noinline void __init arc_ioc_setup(void)
{
unsigned int ioc_base, mem_sz;

+ /*
+ * As for today we don't support both IOC and ZONE_HIGHMEM enabled
+ * simultaneously. This happens because as of today IOC aperture covers
+ * only ZONE_NORMAL (low mem) and any dma transactions outside this
+ * region won't be HW coherent.
+ * If we want to use both IOC and ZONE_HIGHMEM we can use
+ * bounce_buffer to handle dma transactions to HIGHMEM.
+ * Also it is possible to modify dma_direct cache ops or increase IOC
+ * aperture size if we are planning to use HIGHMEM without PAE.
+ */
+ if (IS_ENABLED(CONFIG_HIGHMEM))
+ panic("IOC and HIGHMEM can't be used simultaneously");
+
/* Flush + invalidate + disable L1 dcache */
__dc_disable();

--
2.14.4
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