On 13/02/18 08:24, Tomasz Figa wrote:
Hi Vivek,

Thanks for the patch. Please see my comments inline.

On Wed, Feb 7, 2018 at 7:31 PM, Vivek Gautam
<vivek.gau...@codeaurora.org> wrote:
From: Sricharan R <sricha...@codeaurora.org>

The smmu device probe/remove and add/remove master device callbacks
gets called when the smmu is not linked to its master, that is without
the context of the master device. So calling runtime apis in those places
separately.

Signed-off-by: Sricharan R <sricha...@codeaurora.org>
[vivek: Cleanup pm runtime calls]
Signed-off-by: Vivek Gautam <vivek.gau...@codeaurora.org>
---
  drivers/iommu/arm-smmu.c | 42 ++++++++++++++++++++++++++++++++++++++----
  1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 9e2f917e16c2..c024f69c1682 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -913,11 +913,15 @@ static void arm_smmu_destroy_domain_context(struct 
iommu_domain *domain)
         struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
         struct arm_smmu_device *smmu = smmu_domain->smmu;
         struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
-       int irq;
+       int ret, irq;

         if (!smmu || domain->type == IOMMU_DOMAIN_IDENTITY)
                 return;

+       ret = pm_runtime_get_sync(smmu->dev);
+       if (ret)
+               return;

pm_runtime_get_sync() will return 0 if the device was powered off, 1
if it was already/still powered on or runtime PM is not compiled in,
or a negative value on error, so shouldn't the test be (ret < 0)?

Moreover, I'm actually wondering if it makes any sense to power up the
hardware just to program it and power it down again. In a system where
the IOMMU is located within a power domain, it would cause the IOMMU
block to lose its state anyway.

This is generally for the case where the SMMU internal state remains active, but the programming interface needs to be powered up in order to access it.

Actually, reflecting back on "[PATCH v7 2/6] iommu/arm-smmu: Add
pm_runtime/sleep ops", perhaps it would make more sense to just
control the clocks independently of runtime PM? Then, runtime PM could
be used for real power management, e.g. really powering the block up
and down, for further power saving.

Unfortunately that ends up pretty much unmanageable, because there are numerous different SMMU microarchitectures with fundamentally different clock/power domain schemes (multiplied by individual SoC integration possibilities). Since this is fundamentally a generic architectural driver, adding explicit clock support would probably make the whole thing about 50% clock code, with complicated decision trees around every hardware access calculating which clocks are necessary for a given operation on a given system. That maintainability aspect is why we've already nacked such a fine-grained approach in the past.

Robin.
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