[RFC PATCH 4/9] iommu/rockchip: skip orphaned-fault banks in rk_iommu_is_stall_active

[Jiaxing Hu <gahing@gahingwoo.com>]

Boot firmware can leave a PAGE_FAULT_ACTIVE condition in an IOMMU bank
before the driver has configured paging.  Such a bank shows:

  PAGE_FAULT_ACTIVE=1  STALL_ACTIVE=0  IDLE=1

rk_iommu_is_stall_active() sees STALL_ACTIVE=0 and reports the whole
IOMMU as "not stalled", so any subsequent readx_poll_timeout() loop
waiting for the stall to complete never sees a passing result even
after the other banks have correctly entered stall mode.

Detect the orphaned-fault pattern (PAGE_FAULT_ACTIVE & !STALL_ACTIVE &
IDLE) and skip those banks in the stall check.  They have no in-flight
transaction, so they are already quiescent.

Signed-off-by: Jiaxing Hu <gahing@gahingwoo.com>
---
 drivers/iommu/rockchip-iommu.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index 0013cf196..f42ffcafb 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -378,9 +378,23 @@ static bool rk_iommu_is_stall_active(struct rk_iommu *iommu)
 	bool active = true;
 	int i;
 
-	for (i = 0; i < iommu->num_mmu; i++)
-		active &= !!(rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
-					   RK_MMU_STATUS_STALL_ACTIVE);
+	for (i = 0; i < iommu->num_mmu; i++) {
+		u32 status = rk_iommu_read(iommu->bases[i], RK_MMU_STATUS);
+
+		/*
+		 * A bank stuck with PAGE_FAULT_ACTIVE but without STALL_ACTIVE
+		 * and with IDLE set has an orphaned fault left by firmware before
+		 * paging was configured.  It cannot enter stall mode but has no
+		 * transaction in flight, so it is already quiescent.  Skip it
+		 * rather than treating it as "not stalled."
+		 */
+		if ((status & RK_MMU_STATUS_PAGE_FAULT_ACTIVE) &&
+		    !(status & RK_MMU_STATUS_STALL_ACTIVE) &&
+		    (status & RK_MMU_STATUS_IDLE))
+			continue;
+
+		active &= !!(status & RK_MMU_STATUS_STALL_ACTIVE);
+	}
 
 	return active;
 }
-- 
2.43.0