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 -- 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
