[PATCH] iommu/arm-smmu-v3: Convert to use atomic poll timeout

[Pranjal Shrivastava <praan@google.com>]

The arm_smmu_write_reg_sync() helper is currently implemented using
readl_relaxed_poll_timeout() (that relies on usleep_range() internally)
which becomes a critical issue when used in the gerror irq handler.

If the SMMU hits a gerror and enters Service Failure Mode
(GERROR_SFM_ERR), the gerror handler calls arm_smmu_device_disable() in
hard-irq context. This becomes a problem as arm_smmu_device_disable()
inevitably calls arm_smmu_write_reg_sync() which might attempt to sleep
inside a hard-irq context.

Fix this by converting the arm_smmu_write_reg_sync to use the
readl_relaxed_poll_timeout_atomic() polling helper.

(Discovered while running Sashiko locally on another patch series).

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 48ec83bcbcf5 ("iommu/arm-smmu: Add initial driver support for ARM SMMUv3 devices")
Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index a10affb483a4..f8f8193d0830 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4533,8 +4533,9 @@ static int arm_smmu_write_reg_sync(struct arm_smmu_device *smmu, u32 val,
 	u32 reg;
 
 	writel_relaxed(val, smmu->base + reg_off);
-	return readl_relaxed_poll_timeout(smmu->base + ack_off, reg, reg == val,
-					  1, ARM_SMMU_POLL_TIMEOUT_US);
+	return readl_relaxed_poll_timeout_atomic(smmu->base + ack_off, reg,
+						reg == val, 1,
+						ARM_SMMU_POLL_TIMEOUT_US);
 }
 
 /* GBPA is "special" */
-- 
2.55.0.487.gaf234c4eb3-goog