ARC: IOC: panic if both IOC and ZONE_HIGHMEM enabled

Eugeniy Paltsev · vineetgarc · commit 2b720e99a129 · 2018-09-04T13:21:37.000-07:00
Signed-off-by: Eugeniy Paltsev &lt;Eugeniy.Paltsev@synopsys.com&gt;
Signed-off-by: Vineet Gupta &lt;vgupta@synopsys.com&gt;
diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
@@ -1144,6 +1144,19 @@ 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();
 
