Re: [PATCH] iommu/arm-smmu: fix "hang" when games exit

From: Robin Murphy
Date: Tue Sep 10 2019 - 11:01:43 EST

On 07/09/2019 18:50, Rob Clark wrote:
From: Rob Clark <robdclark@xxxxxxxxxxxx>

When games, browser, or anything using a lot of GPU buffers exits, there
can be many hundreds or thousands of buffers to unmap and free. If the
GPU is otherwise suspended, this can cause arm-smmu to resume/suspend
for each buffer, resulting 5-10 seconds worth of reprogramming the
context bank (arm_smmu_write_context_bank()/arm_smmu_write_s2cr()/etc).
To the user it would appear that the system is locked up.

A simple solution is to use pm_runtime_put_autosuspend() instead, so we
don't immediately suspend the SMMU device.

Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
Note: I've tied the autosuspend enable/delay to the consumer device,
based on the reasoning that if the consumer device benefits from using
an autosuspend delay, then it's corresponding SMMU probably does too.
Maybe that is overkill and we should just unconditionally enable

I'm not sure there's really any reason to expect that a supplier's usage model when doing things for itself bears any relation to that of its consumer(s), so I'd certainly lean towards the "unconditional" argument myself.

Of course ideally we'd skip resuming altogether in the map/unmap paths (since resume implies a full TLB reset anyway), but IIRC that approach started to get messy in the context of the initial RPM patchset. I'm planning to fiddle around a bit more to clean up the implementation of the new iommu_flush_ops stuff, so I've made a note to myself to revisit RPM to see if there's a sufficiently clean way to do better. In the meantime, though, I don't have any real objection to using some reasonable autosuspend delay on the principle that if we've been woken up to map/unmap one page, there's a high likelihood that more will follow in short order (and in the configuration slow-paths it won't have much impact either way).


drivers/iommu/arm-smmu.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index c2733b447d9c..73a0dd53c8a3 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -289,7 +289,7 @@ static inline int arm_smmu_rpm_get(struct arm_smmu_device *smmu)
static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
if (pm_runtime_enabled(smmu->dev))
- pm_runtime_put(smmu->dev);
+ pm_runtime_put_autosuspend(smmu->dev);
static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
@@ -1445,6 +1445,15 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
/* Looks ok, so add the device to the domain */
ret = arm_smmu_domain_add_master(smmu_domain, fwspec);
+#ifdef CONFIG_PM
+ /* TODO maybe device_link_add() should do this for us? */
+ if (dev->power.use_autosuspend) {
+ pm_runtime_set_autosuspend_delay(smmu->dev,
+ dev->power.autosuspend_delay);
+ pm_runtime_use_autosuspend(smmu->dev);
+ }
return ret;