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? Quoting Tomasz once again here: >>> 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 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. Regards Vivek > > Best regards, > Tomasz > >> >>> >>> 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 -- 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 devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
