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? > > a) For IRQ context, the master is already powered on and so the SMMU > is also powered on, through respective device link. > pm_runtime_get_sync() would ultimately just increment the runtime PM > usage count. > > b) For a case when the master is already powered off (which wouldn't > be IRQ context, for the reason stated in a)), powering on the SMMU is > unavoidable, if the SMMU hardware really needs to be accessed (i.e. > some TLBs need to be invalidated, if their state is preserved despite > master being powered down). > >> >>> >>>> >>>> There has already been some discussion about this on various earlier >>>> permutations of this patchset. I think we have exhausted all other >>>> options. >>> >>> I guess I should have read those. Let me do that now. >> Yea, i point to the thread in cover letter and [PATCH 1/6]. >> Thanks. > > I read through all the links in the cover letter and I could see other > attempts not working out indeed, but they were different from what I'm > proposing. > > There was also a point raised that __pm_runtime_resume() called from > pm_runtime_get_sync() would grab dev->power_lock spinlock, which is > true, except that if the device is already active, it would do it only > for the time of checking device state, so I doubt it would really be a > significant point of contention. > > Best regards, > Tomasz > -- > To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
