On Tue, 2015-02-24 at 14:34 -0600, Scott Wood wrote:

On Fri, 2015-02-20 at 19:35 +1100, Benjamin Herrenschmidt wrote:

quoted

@@ -149,14 +141,13 @@ static void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sg,
 
 static int dma_direct_dma_supported(struct device *dev, u64 mask)
 {
-#ifdef CONFIG_PPC64
-	/* Could be improved so platforms can set the limit in case
-	 * they have limited DMA windows
-	 */
-	return mask >= get_dma_offset(dev) + (memblock_end_of_DRAM() - 1);
-#else
-	return 1;
+	u64 offset = get_dma_offset(dev);
+	u64 limit = offset + memblock_end_of_DRAM() - 1;
+
+#if defined(CONFIG_ZONE_DMA32)
+	limit = offset + dma_get_zone_limit(ZONE_DMA32);
 #endif
+	return mask >= limit;
 }

I'm confused as to whether dma_supported() is supposed to be testing a
coherent mask or regular mask...  The above suggests coherent, as does
the call to dma_supported() in dma_set_coherent_mask(), but if swiotlb
is used, swiotlb_dma_supported() will only check for a mask that can
accommodate io_tlb_end, without regard for coherent allocations.

This is confusing indeed, but without the above, dma_set_coherent_mask()
won't work ... so I'm assuming the above. Notice that x86 doesn't even
bother and basically return 1 for anything above a 24 bit mask (appart
from the force_sac case but we can ignore it).

So we probably should fix our swiotlb implementation as well... but
that's orthogonal.

quoted

 static u64 dma_direct_get_required_mask(struct device *dev)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index f146ef0..a7f15e2 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c

@@ -277,6 +277,11 @@ int dma_pfn_limit_to_zone(u64 pfn_limit)
 	return -EPERM;
 }
 
+u64 dma_get_zone_limit(int zone)
+{
+	return max_zone_pfns[zone] << PAGE_SHIFT;
+}

If you must do this in terms of bytes rather than pfn, cast to u64
before shifting -- and even then the result will be PAGE_SIZE - 1 too
small.

Do we have RAM above what a unsigned long can hold ? I think I'll just
make it a pfn and respin...

Cheers,
Ben.

-Scott