[RFC PATCH v2 5/8] iommu/rockchip: clear stale page faults before enabling stall

[Jiaxing Hu]

Boot firmware can leave an IOMMU bank in PAGE_FAULT_ACTIVE before the
driver has configured paging:

  PAGE_FAULT_ACTIVE=1  STALL_ACTIVE=0  IDLE=1

Such a bank ignores CMD_ENABLE_STALL and never reaches STALL_ACTIVE, so
rk_iommu_enable_stall()'s readx_poll_timeout() spins until it times out
(seen on the RK3576 NPU, whose MMUs share this poll across banks).

Rather than special-casing these banks in the stall path, acknowledge the
stale fault with CMD_PAGE_FAULT_DONE before enabling stall, so every bank
starts from a clean state and the normal stall sequence applies to all of
them.  Banks without a pending fault are untouched.

Signed-off-by: Jiaxing Hu <gahing at gahingwoo.com>
---
 drivers/iommu/rockchip-iommu.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index 62cd6b022..68bd55433 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -415,6 +415,19 @@ static int rk_iommu_enable_stall(struct rk_iommu *iommu)
 	if (!rk_iommu_is_paging_enabled(iommu))
 		return 0;
 
+	/*
+	 * Boot firmware can leave a bank in PAGE_FAULT_ACTIVE with no handler
+	 * (PAGE_FAULT_ACTIVE & !STALL_ACTIVE & IDLE).  Such a bank ignores
+	 * CMD_ENABLE_STALL and never reaches STALL_ACTIVE, timing out the poll
+	 * below.  Acknowledge any stale fault first so every bank starts clean.
+	 */
+	for (i = 0; i < iommu->num_mmu; i++) {
+		if (rk_iommu_read(iommu->bases[i], RK_MMU_STATUS) &
+		    RK_MMU_STATUS_PAGE_FAULT_ACTIVE)
+			writel(RK_MMU_CMD_PAGE_FAULT_DONE,
+			       iommu->bases[i] + RK_MMU_COMMAND);
+	}
+
 	rk_iommu_command(iommu, RK_MMU_CMD_ENABLE_STALL);
 
 	ret = readx_poll_timeout(rk_iommu_is_stall_active, iommu, val,
-- 
2.43.0