Hi Will,
On 2021-01-06 17:26, Will Deacon wrote:
On Thu, Dec 24, 2020 at 12:10:07PM +0530, Sai Prakash Ranjan wrote:
commit ecd7274fb4cd ("iommu: Remove unused IOMMU_SYS_CACHE_ONLY flag")
removed unused IOMMU_SYS_CACHE_ONLY prot flag and along with it went
the memory type setting required for the non-coherent masters to use
system cache. Now that system cache support for GPU is added, we will
need to mark the memory as normal sys-cached for GPU to use system
cache.
Without this, the system cache lines are not allocated for GPU. We use
the IO_PGTABLE_QUIRK_ARM_OUTER_WBWA quirk instead of a page protection
flag as the flag cannot be exposed via DMA api because of no in-tree
users.
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
---
drivers/iommu/io-pgtable-arm.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/iommu/io-pgtable-arm.c
b/drivers/iommu/io-pgtable-arm.c
index 7c9ea9d7874a..3fb7de8304a2 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 (data->iop.cfg.quirks & IO_PGTABLE_QUIRK_ARM_OUTER_WBWA)
+ pte |= (ARM_LPAE_MAIR_ATTR_IDX_INC_OCACHE
+ << ARM_LPAE_PTE_ATTRINDX_SHIFT);
}
drivers/iommu/io-pgtable.c currently documents this quirk as applying
only
to the page-table walker. Given that we only have one user at the
moment,
I think it's ok to change that, but please update the comment.
Sure, how about this change in comment:
* IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the
outer-cacheability
- * attributes set in the TCR for a non-coherent page-table
walker.
+ * attributes set in the TCR for a non-coherent page-table
walker
+ * and also to set the correct cacheability attributes to
use an
+ * outer level of cache for non-coherent masters.
We also need to decide on whether we want to allow the quirk to be
passed
if the coherency of the page-table walker differs from the DMA device,
since
we have these combinations:
Coherent walker? IOMMU_CACHE IO_PGTABLE_QUIRK_ARM_OUTER_WBWA
0: N 0 0
1: N 0 1
2: N 1 0
3: N 1 1
4: Y 0 0
5: Y 0 1
6: Y 1 0
7: Y 1 1
Some of them are obviously bogus, such as (7), but I don't know what to
do about cases such as (3) and (5).
I thought this was already decided when IOMMU_SYS_CACHE_ONLY prot flag
was
added in this same location [1]. dma-coherent masters can use the normal
cached memory type to use the system cache and non dma-coherent masters
willing to use system cache should use normal sys-cached memory type
with
this quirk.
[1]
https://lore.kernel.org/linux-arm-msm/20190516093020.18028-1-vivek.gautam@xxxxxxxxxxxxxx/
Thanks,
Sai
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