Re: [PATCH v7 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device

[Vivek Gautam <vivek.gautam-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On Fri, Feb 23, 2018 at 9:10 PM, Jordan Crouse <jcrouse@codeaurora.org> wrote:
> On Fri, Feb 23, 2018 at 04:06:39PM +0530, Vivek Gautam wrote:
>> On Fri, Feb 23, 2018 at 5:22 AM, Jordan Crouse <jcrouse@codeaurora.org> wrote:
>> > On Wed, Feb 07, 2018 at 04:01:19PM +0530, Vivek Gautam wrote:
>> >> From: Sricharan R <sricharan@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 <sricharan@codeaurora.org>
>> >> [vivek: Cleanup pm runtime calls]
>> >> Signed-off-by: Vivek Gautam <vivek.gautam@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;
>> >> +
>> >>       /*
>> >>        * Disable the context bank and free the page tables before freeing
>> >>        * it.
>> >> @@ -932,6 +936,8 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>> >>
>> >>       free_io_pgtable_ops(smmu_domain->pgtbl_ops);
>> >>       __arm_smmu_free_bitmap(smmu->context_map, cfg->cbndx);
>> >> +
>> >> +     pm_runtime_put_sync(smmu->dev);
>> >>  }
>> >>
>> >>  static struct iommu_domain *arm_smmu_domain_alloc(unsigned type)
>> >> @@ -1407,14 +1413,22 @@ static int arm_smmu_add_device(struct device *dev)
>> >>       while (i--)
>> >>               cfg->smendx[i] = INVALID_SMENDX;
>> >>
>> >> -     ret = arm_smmu_master_alloc_smes(dev);
>> >> +     ret = pm_runtime_get_sync(smmu->dev);
>> >>       if (ret)
>> >>               goto out_cfg_free;
>> >
>> > Hey Vivek, I just hit a problem with this on sdm845. It turns out that
>> > pm_runtime_get_sync() returns a positive 1 if the device is already active.
>> >
>> > I hit this in the GPU code. The a6xx has two platform devices that each use a
>> > different sid on the iommu. The GPU is probed normally from a platform driver
>> > and it in turn initializes the GMU device by way of a phandle.
>> >
>> > Because the GMU isn't probed with a platform driver we need to call
>> > of_dma_configure() on the device to set up the IOMMU for the device which ends
>> > up calling through this path and we discover that the smmu->dev is already
>> > powered (pm_runtime_get_sync returns 1).
>> >
>> > I'm not immediately sure if this is a bug on sdm845 or not because a cursory
>> > inspection says that the SMMU device shouldn't be powered at this time but there
>> > might be a connection that I'm not seeing. Obviously if the SMMU was left
>> > powered thats a bad thing. But putting that aside it is obvious that this
>> > code should be accommodating of the possibility that the device is already
>> > powered, and so this should be
>> >
>> > if (ret < 0)
>> >         goto out_cfg_free;
>>
>> Right, as Tomasz also pointed, we should surely check the negative value of
>> pm_runtime_get_sync().
>
> Sorry, I didn't notice that Tomasz had pointed it out as well. I wanted to
> quickly get it on the mailing list so you could catch it in your time zone.
>
>> From your description, it may be that the GPU has turned on the smmu, and
>> then once if goes and probes the GMU, the GMU device also wants to turn-on
>> the same smmu device. But that's already active. So pm_runtime_get_sync()
>> returns 1.
>> Am i making sense?
>
> My concern is that this is happening during the probe and we shouldn't be
> energizing the GPU at this point. But it is entirely possible that the
> bus is on for other reasons. I'll do a bit of digging today and see exactly
> which device is at fault.

I will try to check it myself too.

regards
Vivek
>
>
> Jordan
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