On Thu, Feb 15, 2018 at 1:03 AM, Robin Murphy <robin.murphy@xxxxxxx> wrote: > On 14/02/18 10:33, Vivek Gautam wrote: >> >> On Wed, Feb 14, 2018 at 2:46 PM, Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: >> >> Adding Jordan to this thread as well. >> >>> On Wed, Feb 14, 2018 at 6:13 PM, Vivek Gautam >>> <vivek.gautam@xxxxxxxxxxxxxx> wrote: >>>> >>>> Hi Tomasz, >>>> >>>> On Wed, Feb 14, 2018 at 11:08 AM, Tomasz Figa <tfiga@xxxxxxxxxxxx> >>>> wrote: >>>>> >>>>> On Wed, Feb 14, 2018 at 1:17 PM, Vivek Gautam >>>>> <vivek.gautam@xxxxxxxxxxxxxx> wrote: >>>>>> >>>>>> Hi Tomasz, >>>>>> >>>>>> On Wed, Feb 14, 2018 at 8:31 AM, Tomasz Figa <tfiga@xxxxxxxxxxxx> >>>>>> wrote: >>>>>>> >>>>>>> On Wed, Feb 14, 2018 at 11:13 AM, Rob Clark <robdclark@xxxxxxxxx> >>>>>>> wrote: >>>>>>>> >>>>>>>> On Tue, Feb 13, 2018 at 8:59 PM, Tomasz Figa <tfiga@xxxxxxxxxxxx> >>>>>>>> wrote: >>>>>>>>> >>>>>>>>> On Wed, Feb 14, 2018 at 3:03 AM, Rob Clark <robdclark@xxxxxxxxx> >>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> On Tue, Feb 13, 2018 at 4:10 AM, Tomasz Figa <tfiga@xxxxxxxxxxxx> >>>>>>>>>> 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@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> >>>>>>>>>>>> --- >>>>>>>>>>>> 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. Could you elaborate on what kind of locking you are concerned about? As I explained before, the normally happening fast path would lock dev->power_lock only for the brief moment of incrementing the runtime PM usage counter. Best regards, Tomasz -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
