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iommu/arm-smmu: Avoid pathological RPM behaviour for unmaps 

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 just locked up.

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

Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Rob Clark 2019-10-31 14:31:02 -07:00 committed by Will Deacon
parent bdde4718ab
commit ee9bdfedd3
1 changed files with 15 additions and 1 deletions
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16
drivers/iommu/arm-smmu.c
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@ -123,7 +123,7 @@ 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)
@ -1167,6 +1167,20 @@ 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);
/*
* Setup an autosuspend delay to avoid bouncing runpm state.
* Otherwise, if a driver for a suspended consumer device
* unmaps buffers, it will runpm resume/suspend for each one.
*
* For example, when used by a GPU device, when an application
* or game exits, it can trigger unmapping 100s or 1000s of
* buffers. With a runpm cycle for each buffer, that adds up
* to 5-10sec worth of reprogramming the context bank, while
* the system appears to be locked up to the user.
*/
pm_runtime_set_autosuspend_delay(smmu->dev, 20);
pm_runtime_use_autosuspend(smmu->dev);
rpm_put:
arm_smmu_rpm_put(smmu);
return ret;