On 2021-01-29 14:35, Will Deacon wrote:
On Mon, Jan 11, 2021 at 07:45:04PM +0530, Sai Prakash Ranjan wrote:
Add a new page protection flag IOMMU_LLC which can be used
by non-coherent masters to set cacheable memory attributes
for an outer level of cache called as last-level cache or
system cache. Initial user of this page protection flag is
the adreno gpu and then can later be used by other clients
such as video where this can be used for per-buffer based
mapping.
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
---
drivers/iommu/io-pgtable-arm.c | 3 +++
include/linux/iommu.h | 6 ++++++
2 files changed, 9 insertions(+)
diff --git a/drivers/iommu/io-pgtable-arm.c
b/drivers/iommu/io-pgtable-arm.c
index 7439ee7fdcdb..ebe653ef601b 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -415,6 +415,9 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct
arm_lpae_io_pgtable *data,
else if (prot & IOMMU_CACHE)
pte |= (ARM_LPAE_MAIR_ATTR_IDX_CACHE
<< ARM_LPAE_PTE_ATTRINDX_SHIFT);
+ else if (prot & IOMMU_LLC)
+ pte |= (ARM_LPAE_MAIR_ATTR_IDX_INC_OCACHE
+ << ARM_LPAE_PTE_ATTRINDX_SHIFT);
}
if (prot & IOMMU_CACHE)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ffaa389ea128..1f82057df531 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -31,6 +31,12 @@
* if the IOMMU page table format is equivalent.
*/
#define IOMMU_PRIV (1 << 5)
+/*
+ * Non-coherent masters can use this page protection flag to set
cacheable
+ * memory attributes for only a transparent outer level of cache,
also known as
+ * the last-level or system cache.
+ */
+#define IOMMU_LLC (1 << 6)
On reflection, I'm a bit worried about exposing this because I think it
will
introduce a mismatched virtual alias with the CPU (we don't even have a
MAIR
set up for this memory type). Now, we also have that issue for the PTW,
but
since we always use cache maintenance (i.e. the streaming API) for
publishing the page-tables to a non-coheren walker, it works out.
However,
if somebody expects IOMMU_LLC to be coherent with a DMA API coherent
allocation, then they're potentially in for a nasty surprise due to the
mismatched outer-cacheability attributes.
Can't we add the syscached memory type similar to what is done on
android?
So I can take patch (1) as a trivial rename, but unfortunately I think
this
needs more thought before exposing it beyond the PTW.
That wouldn't be of much use, would it :) , we would be losing on
perf gain for GPU usecases without the rest of the patches.
Thanks,
Sai
--
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