[RFC PATCH v5 08/10] iommu/riscv: Pre-enable GADE for second-stage domains

[fangyu.yu at linux.alibaba.com]

From: Fangyu Yu <fangyu.yu at 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 at linux.alibaba.com>
---
 drivers/iommu/riscv/iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index debce1b4201c..9310b818c038 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -1236,6 +1236,8 @@ static void riscv_iommu_iodir_update(struct riscv_iommu_device *iommu,
 	for (i = 0; i < fwspec->num_ids; i++) {
 		dc = riscv_iommu_get_dc(iommu, fwspec->ids[i]);
 		tc = READ_ONCE(dc->tc);
+		tc &= ~RISCV_IOMMU_DC_TC_GADE;
+		tc |= new_dc->tc & RISCV_IOMMU_DC_TC_GADE;
 		tc |= new_dc->ta & RISCV_IOMMU_DC_TC_V;
 
 		WRITE_ONCE(dc->fsc, new_dc->fsc);
@@ -1352,6 +1354,8 @@ 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