linux-kernel - Re: [PATCH 1/1] base: power: runtime: Export pm_runtime_get/put

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Message-ID: <CAFp+6iHp5dt80p6-cMKLbcoHLfkRjVztFn8N2kiB24dUeeHpMA@mail.gmail.com>
Date:   Fri, 8 Dec 2017 19:09:11 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
        linux-pm@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 1/1] base: power: runtime: Export pm_runtime_get/put_suppliers

Hi Greg,


On Fri, Dec 8, 2017 at 6:51 PM, Greg KH <gregkh@...uxfoundation.org> 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@...eaurora.org>
>> ---
>>  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;
  }


regards
Vivek

>
> thanks,
>
> greg k-h



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