Re: [PATCH 1/1] iommu/arm-smmu-qcom: remove runtime pm enabling for TBU driver

[Zhenhua Huang]

On 2024/8/13 15:20, Pranjal Shrivastava wrote:
> On Tue, Aug 13, 2024 at 10:37:33AM +0800, Zhenhua Huang wrote:
> > On 2024/8/12 21:25, Pranjal Shrivastava wrote:
> > > On Tue, Jul 30, 2024 at 06:30:43PM +0800, Zhenhua Huang wrote:
> > > > TBU driver has no runtime pm support now, adding pm_runtime_enable()
> > > > seems to be useless. Remove it.
> > > >
> > > > Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
> > > > ---
> > > >    drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 6 ------
> > > >    1 file changed, 6 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > > index 36c6b36ad4ff..aff2fe1fda13 100644
> > > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> > > > @@ -566,7 +566,6 @@ static struct acpi_platform_list qcom_acpi_platlist[] = {
> > > >    static int qcom_smmu_tbu_probe(struct platform_device *pdev)
> > > >    {
> > > > -	struct device *dev = &pdev->dev;
> > > >    	int ret;
> > > >    	if (IS_ENABLED(CONFIG_ARM_SMMU_QCOM_DEBUG)) {
> > > > @@ -575,11 +574,6 @@ static int qcom_smmu_tbu_probe(struct platform_device *pdev)
> > > >    			return ret;
> > > >    	}
> > > > -	if (dev->pm_domain) {
> > > > -		pm_runtime_set_active(dev);
> > > > -		pm_runtime_enable(dev);
> > >
> > > I assumed that this was required to avoid the TBU from being powered
> > > down? If so, then I think we shall move it under the
> >
> > Hi Pranjal,
> >
> > In my sense, this was giving the TBU ability to power down when
> > necessary(through pm callbacks)? While I haven't seen any RPM impl for TBU
> > device.. hence having the doubt..
> >
> > Thanks,
> > Zhenhua
>
> Apologies for being unclear. I just meant to ask if there was a reason
> to add pm_runtime_set_active & enable in the tbu probe previously? And I

It's also my doubt and hope Georgi can help clarify :)
Actually I assume this part of codes was copied from arm-smmu driver
https://elixir.bootlin.com/linux/v6.11-rc3/source/drivers/iommu/arm/arm-smmu/arm-smmu.c#L2264 
.. but for TBU, seems no user ?

> *assumed* that it was to set the device state as RPM_ACTIVE to avoid it
> being RPM_SUSPENDED after enabling pm_runtime

Yeah, it's normal sequence from doc: 
https://elixir.bootlin.com/linux/v6.11-rc3/source/Documentation/power/runtime_pm.rst#L574

> I agree that there are no pm_runtime_suspend/resume calls within the TBU
> driver. I'm just trying to understand why was pm_runtime enabled here
> earlier (since it's not implemented) in order to ensure that removing it
> doesn't cause further troubles?

See above my assumption, need Georgi to comment but.

> I see Georgi added it as a part of
> https://lore.kernel.org/all/20240704010759.507798-1-quic_c_gdjako@xxxxxxxxxxx/
>
> But I'm unsure why was it required to fix that bug?

I'm just thinking it is dead code and want to see if my understanding is 
correct.

Thanks,
Zhenhua

> > > previous if condition, i.e. CONFIG_ARM_SMMU_QCOM_DEBUG?
> > >
> > > If not, we can remove it give that the TBU would be powered ON as needed
> > >
> > > > -	}
> > > > -
> > > >    	return 0;
> > > >    }
> > > > --
> > > > 2.7.4
> > >
> > > Thanks,
> > > Pranjal
>
> Thanks,
> Pranjal