[RFC PATCH 5/9] iommu/rockchip: skip orphaned-fault banks in CMD_ENABLE_STALL dispatch

[Jiaxing Hu]

Sending CMD_ENABLE_STALL to a bank that carries an orphaned firmware
fault (PAGE_FAULT_ACTIVE & !STALL_ACTIVE & IDLE) causes the command to
be silently dropped by that bank.  The dropped command also interferes
with the other banks' stall transition, delaying them past the poll
timeout even though they would otherwise stall within a few
microseconds.

Skip such banks when issuing CMD_ENABLE_STALL, matching the skip
condition already used in rk_iommu_is_stall_active().

Signed-off-by: Jiaxing Hu <gahing@xxxxxxxxxxxxx>
---
 drivers/iommu/rockchip-iommu.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index f42ffcafb..ce586919b 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -434,7 +434,21 @@ static int rk_iommu_enable_stall(struct rk_iommu *iommu)
 	if (!rk_iommu_is_paging_enabled(iommu))
 		return 0;
 
-	rk_iommu_command(iommu, RK_MMU_CMD_ENABLE_STALL);
+	/*
+	 * Do not send CMD_ENABLE_STALL to orphaned-fault banks
+	 * (PAGE_FAULT_ACTIVE & !STALL_ACTIVE & IDLE): the command is ignored
+	 * by such a bank but its presence on the shared bus delays the other
+	 * banks from reaching STALL_ACTIVE within the poll timeout.
+	 */
+	for (i = 0; i < iommu->num_mmu; i++) {
+		u32 status = rk_iommu_read(iommu->bases[i], RK_MMU_STATUS);
+
+		if ((status & RK_MMU_STATUS_PAGE_FAULT_ACTIVE) &&
+		    !(status & RK_MMU_STATUS_STALL_ACTIVE) &&
+		    (status & RK_MMU_STATUS_IDLE))
+			continue;
+		writel(RK_MMU_CMD_ENABLE_STALL, iommu->bases[i] + RK_MMU_COMMAND);
+	}
 
 	ret = readx_poll_timeout(rk_iommu_is_stall_active, iommu, val,
 				 val, RK_MMU_POLL_PERIOD_US,
-- 
2.43.0