Messages in this thread | | | Subject | Re: [PATCH v7 6/6] drm/msm: iommu: Replace runtime calls with runtime suppliers | From | Robin Murphy <> | Date | Wed, 14 Feb 2018 16:03:39 +0000 |
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On 14/02/18 10:33, Vivek Gautam wrote: > On Wed, Feb 14, 2018 at 2:46 PM, Tomasz Figa <tfiga@chromium.org> wrote: > > Adding Jordan to this thread as well. > >> On Wed, Feb 14, 2018 at 6:13 PM, Vivek Gautam >> <vivek.gautam@codeaurora.org> wrote: >>> Hi Tomasz, >>> >>> On Wed, Feb 14, 2018 at 11:08 AM, Tomasz Figa <tfiga@chromium.org> wrote: >>>> On Wed, Feb 14, 2018 at 1:17 PM, Vivek Gautam >>>> <vivek.gautam@codeaurora.org> wrote: >>>>> Hi Tomasz, >>>>> >>>>> On Wed, Feb 14, 2018 at 8:31 AM, Tomasz Figa <tfiga@chromium.org> wrote: >>>>>> On Wed, Feb 14, 2018 at 11:13 AM, Rob Clark <robdclark@gmail.com> wrote: >>>>>>> On Tue, Feb 13, 2018 at 8:59 PM, Tomasz Figa <tfiga@chromium.org> wrote: >>>>>>>> On Wed, Feb 14, 2018 at 3:03 AM, Rob Clark <robdclark@gmail.com> wrote: >>>>>>>>> On Tue, Feb 13, 2018 at 4:10 AM, Tomasz Figa <tfiga@chromium.org> wrote: >>>>>>>>>> Hi Vivek, >>>>>>>>>> >>>>>>>>>> Thanks for the patch. Please see my comments inline. >>>>>>>>>> >>>>>>>>>> On Wed, Feb 7, 2018 at 7:31 PM, Vivek Gautam >>>>>>>>>> <vivek.gautam@codeaurora.org> wrote: >>>>>>>>>>> While handling the concerned iommu, there should not be a >>>>>>>>>>> need to power control the drm devices from iommu interface. >>>>>>>>>>> If these drm devices need to be powered around this time, >>>>>>>>>>> the respective drivers should take care of this. >>>>>>>>>>> >>>>>>>>>>> Replace the pm_runtime_get/put_sync(<drm_device>) with >>>>>>>>>>> pm_runtime_get/put_suppliers(<drm_device>) calls, to power-up >>>>>>>>>>> the connected iommu through the device link interface. >>>>>>>>>>> In case the device link is not setup these get/put_suppliers() >>>>>>>>>>> calls will be a no-op, and the iommu driver should take care of >>>>>>>>>>> powering on its devices accordingly. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org> >>>>>>>>>>> --- >>>>>>>>>>> drivers/gpu/drm/msm/msm_iommu.c | 16 ++++++++-------- >>>>>>>>>>> 1 file changed, 8 insertions(+), 8 deletions(-) >>>>>>>>>>> >>>>>>>>>>> diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c >>>>>>>>>>> index b23d33622f37..1ab629bbee69 100644 >>>>>>>>>>> --- a/drivers/gpu/drm/msm/msm_iommu.c >>>>>>>>>>> +++ b/drivers/gpu/drm/msm/msm_iommu.c >>>>>>>>>>> @@ -40,9 +40,9 @@ static int msm_iommu_attach(struct msm_mmu *mmu, const char * const *names, >>>>>>>>>>> struct msm_iommu *iommu = to_msm_iommu(mmu); >>>>>>>>>>> int ret; >>>>>>>>>>> >>>>>>>>>>> - pm_runtime_get_sync(mmu->dev); >>>>>>>>>>> + pm_runtime_get_suppliers(mmu->dev); >>>>>>>>>>> ret = iommu_attach_device(iommu->domain, mmu->dev); >>>>>>>>>>> - pm_runtime_put_sync(mmu->dev); >>>>>>>>>>> + pm_runtime_put_suppliers(mmu->dev); >>>>>>>>>> >>>>>>>>>> For me, it looks like a wrong place to handle runtime PM of IOMMU >>>>>>>>>> here. iommu_attach_device() calls into IOMMU driver's attach_device() >>>>>>>>>> callback and that's where necessary runtime PM gets should happen, if >>>>>>>>>> any. In other words, driver A (MSM DRM driver) shouldn't be dealing >>>>>>>>>> with power state of device controlled by driver B (ARM SMMU). >>>>>>>>> >>>>>>>>> Note that we end up having to do the same, because of iommu_unmap() >>>>>>>>> while DRM driver is powered off.. it might be cleaner if it was all >>>>>>>>> self contained in the iommu driver, but that would make it so other >>>>>>>>> drivers couldn't call iommu_unmap() from an irq handler, which is >>>>>>>>> apparently something that some of them want to do.. >>>>>>>> >>>>>>>> I'd assume that runtime PM status is already guaranteed to be active >>>>>>>> when the IRQ handler is running, by some other means (e.g. >>>>>>>> pm_runtime_get_sync() called earlier, when queuing some work to the >>>>>>>> hardware). Otherwise, I'm not sure how a powered down device could >>>>>>>> trigger an IRQ. >>>>>>>> >>>>>>>> So, if the master device power is already on, suppliers should be >>>>>>>> powered on as well, thanks to device links. >>>>>>>> >>>>>>> >>>>>>> umm, that is kindof the inverse of the problem.. the problem is >>>>>>> things like gpu driver (and v4l2 drivers that import dma-buf's, >>>>>>> afaict).. they will potentially call iommu->unmap() when device is not >>>>>>> active (due to userspace or things beyond the control of the driver).. >>>>>>> so *they* would want iommu to do pm get/put calls. >>>>>> >>>>>> Which is fine and which is actually already done by one of the patches >>>>>> in this series, not for map/unmap, but probe, add_device, >>>>>> remove_device. Having parts of the API doing it inside the callback >>>>>> and other parts outside sounds at least inconsistent. >>>>>> >>>>>>> But other drivers >>>>>>> trying to unmap from irq ctx would not. Which is the contradictory >>>>>>> requirement that lead to the idea of iommu user powering up iommu for >>>>>>> unmap. >>>>>> >>>>>> Sorry, maybe I wasn't clear. My last message was supposed to show that >>>>>> it's not contradictory at all, because "other drivers trying to unmap >>>>>> from irq ctx" would already have called pm_runtime_get_*() earlier >>>>>> from a non-irq ctx, which would have also done the same on all the >>>>>> linked suppliers, including the IOMMU. The ultimate result would be >>>>>> that the map/unmap() of the IOMMU driver calling pm_runtime_get_sync() >>>>>> would do nothing besides incrementing the reference count. >>>>> >>>>> The entire point was to avoid the slowpath that pm_runtime_get/put_sync() >>>>> would add in map/unmap. It would not be correct to add a slowpath in irq_ctx >>>>> for taking care of non-irq_ctx and for the situations where master is already >>>>> powered-off. >>>> >>>> Correct me if I'm wrong, but I believe that with what I'm proposing >>>> there wouldn't be any slow path. >>> >>> Yea, but only when the power domain is irq-safe? And not all platforms >>> enable irq-safe power domains. For instance, msm doesn't enable its >>> gdsc power domains as irq-safe. >>> Is it something i am missing? >> >> irq-safe would matter if there would exist a case when the call is >> done from IRQ context and the power is off. As I explained in a), it >> shouldn't happen. > > Hi Robin, Will > > Does adding pm_runtime_get() in map/unmap sounds good to you?
Given that we spent significant effort last year removing as much locking as we possibly could from the map/unmap path to minimise the significant performance impact it was having on networking/storage/etc. workloads, I really don't want to introduce more for the sake of one specific use-case, so no.
Robin.
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