[RFC PATCH] iommu: io-pgtable: Drop WARN for empty PTEs on unmap

[Rob Herring <robh@kernel.org>]

If a region has been mapped sparsely (such as on page faults), the user
has to keep track of what was mapped or not in order to avoid warnings
when unmapping the entire region. Remove the WARN on empty PTEs to allow
unmapping sparsely mapped regions.

Cc: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: iommu@lists.linux-foundation.org
Signed-off-by: Rob Herring <robh@kernel.org>
---
This is needed for large (up to 1GB AIUI) scratch buffers on panfrost 
which are mapped on demand on GPU page faults and can be unmapped on 
memory pressure. Alternatively, I'd need to have a bitmap of mapped 
pages to track what is mapped or not. Dropping the WARN seems like a 
much simpler solution.

This will need to go thru the DRM tree once I've gotten the panfrost 
side finished, but wanted some early feedback.

Rob

 drivers/iommu/io-pgtable-arm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 4e21efbc4459..43971638a5aa 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -611,7 +611,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 
 	ptep += ARM_LPAE_LVL_IDX(iova, lvl, data);
 	pte = READ_ONCE(*ptep);
-	if (WARN_ON(!pte))
+	if (!pte)
 		return 0;
 
 	/* If the size matches this level, we're in the right place */
-- 
2.20.1

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