Re: [PATCH 1/1] base: power: runtime: Export pm_runtime_get/put_suppliers

[Vivek Gautam]

Hi Rafael,

On Wed, Jan 3, 2018 at 5:31 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Friday, December 8, 2017 6:03:37 PM CET Vivek Gautam wrote:
>> On Fri, Dec 8, 2017 at 7:37 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>> > On Fri, Dec 8, 2017 at 2:39 PM, Vivek Gautam
>> > <vivek.gautam@xxxxxxxxxxxxxx> wrote:
>> >> Hi Greg,
>> >>
>> >>
>> >> On Fri, Dec 8, 2017 at 6:51 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>> >>> On Fri, Dec 08, 2017 at 06:00:47PM +0530, Vivek Gautam wrote:
>> >>>> The device link allows the pm framework to tie the supplier and
>> >>>> consumer. So, whenever the consumer is powered-on, the supplier
>> >>>> is powered-on first.
>> >>>>
>> >>>> There are however cases in which the consumer wants to power-on
>> >>>> the supplier, but not itself.
>> >>>> E.g., A Graphics or multimedia driver wants to power-on the SMMU
>> >>>> to unmap a buffer and finish the TLB operations without powering
>> >>>> on itself. Some of these unmap requests are coming from the
>> >>>> user space when the controller itself is not powered-up, and it
>> >>>> can be huge penalty in terms of power and latency to power-up
>> >>>> the graphics/mm controllers.
>> >>>> There can be an argument that the supplier should handle this case
>> >>>> on its own and there should not be a need for the consumer to
>> >>>> power-on the supplier. But as discussed on the thread [1] about
>> >>>> ARM-SMMU runtime pm, we don't want to introduce runtime pm calls
>> >>>> in atomic paths, such as in arm_smmu_unmap.
>> >>>>
>> >>>> [1] https://patchwork.kernel.org/patch/9827825/
>> >>>>
>> >>>> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
>> >>>> ---
>> >>>>  drivers/base/power/runtime.c | 2 ++
>> >>>>  1 file changed, 2 insertions(+)
>> >>>>
>> >>>> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
>> >>>> index 027d159ac381..af169304ca13 100644
>> >>>> --- a/drivers/base/power/runtime.c
>> >>>> +++ b/drivers/base/power/runtime.c
>> >>>> @@ -1578,6 +1578,7 @@ void pm_runtime_get_suppliers(struct device *dev)
>> >>>>
>> >>>>       device_links_read_unlock(idx);
>> >>>>  }
>> >>>> +EXPORT_SYMBOL_GPL(pm_runtime_get_suppliers);
>> >>>
>> >>> We do not export symbols unless there are in-kernel users of them.
>> >>> Where is the patch that adds a user for these functions?
>> >>
>> >> My apologies for not putting the changes for the user of these APIs.
>> >> I will be sending a patch for the user (which would be:
>> >> "drivers/gpu/drm/msm/msm_iommu.c"). The patch will be included
>> >> with the arm-smmu runtime patch series. Right now I am facing issues
>> >> with the use of clk_bulk_*() APIs on 4.15-rc kernel.
>> >>
>> >> But, I wanted to get opinions about this change since we had been
>> >> discussing about this in the arm-smmu runtime patch thread [1].
>> >>
>> >> [1] https://patchwork.kernel.org/patch/9827825/
>> >>
>> >>
>> >> P.S.: A snippet of the change in the user of these APIs:
>> >>
>> >>  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
>> >>  @@ -76,9 +76,9 @@ static int msm_iommu_unmap(struct msm_mmu *mmu,
>> >> uint64_t iova,
>> >>   {
>> >>          struct msm_iommu *iommu = to_msm_iommu(mmu);
>> >>
>> >>  -       pm_runtime_get_sync(mmu->dev);
>> >>  +       pm_runtime_get_suppliers(mmu->dev);
>> >>          iommu_unmap(iommu->domain, iova, len);
>> >>  -       pm_runtime_put_sync(mmu->dev);
>> >>  +       pm_runtime_put_suppliers(mmu->dev);
>> >>
>> >>          return 0;
>> >>   }
>> >>
>> >
>> > Well, pm_runtime_get/put_suppliers() were not designed to be used
>> > outside of the runtime PM core code.  I need to have a deeper look
>> > into things at this point, so give me some time.
>>
>> Thanks Rafael.
>
> No problem, sorry for the delay.
>
> It should be OK to export these routines as you proposed, but again,
> please post this patch along with the driver changes depending on it.

Thanks. Sure, i will post the patch as part of the patch series for
the smmu driver.

Regards
Vivek

>
> Thanks,
> Rafael
>



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