[RFC PATCH v4 08/10] iommu/riscv: Pre-enable GADE for second-stage domains

[fangyu.yu@linux.alibaba.com]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Pre-enable RISCV_IOMMU_DC_TC_GADE in the device context when
attaching a second-stage domain, if the IOMMU supports AMO_HWAD.

Software pre-populates second-stage page tables with D set, so
enabling GADE by default does not change normal behavior. When
dirty tracking is enabled, iommufd clears the pre-set D bits and
GADE becomes necessary for hardware to update the dirty bit on
write access.

This avoids toggling GADE dynamically and keeps device context
setup consistent with second-stage domain attachment.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
 drivers/iommu/riscv/iommu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 16779877351b..f01fd4e2f840 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -1330,6 +1330,8 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 			FIELD_PREP(RISCV_IOMMU_DC_IOHGATP_MODE, pt_info.iohgatp_mode) |
 			FIELD_PREP(RISCV_IOMMU_DC_IOHGATP_GSCID, domain->gscid) |
 			FIELD_PREP(RISCV_IOMMU_DC_IOHGATP_PPN, pt_info.ppn);
+		if (iommu->caps & RISCV_IOMMU_CAPABILITIES_AMO_HWAD)
+			dc.tc |= RISCV_IOMMU_DC_TC_GADE;
 	} else {
 		if (!riscv_iommu_fsc_supported(iommu, pt_info.fsc_iosatp_mode))
 			return -ENODEV;
-- 
2.50.1