Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device_link between masters and smmu

[Vivek Gautam]

On 7/17/2018 1:16 PM, Rafael J. Wysocki wrote:
> On Mon, Jul 16, 2018 at 1:46 PM, Vivek Gautam
> <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > On 7/16/2018 2:25 PM, Rafael J. Wysocki wrote:
> > > On Thu, Jul 12, 2018 at 2:41 PM, Vivek Gautam
> > > <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > > > Hi Rafael,
> > > >
> > > >
> > > > On Wed, Jul 11, 2018 at 4:06 PM, Vivek Gautam
> > > > <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > > > > Hi Rafael,
> > > > >
> > > > >
> > > > >
> > > > > On 7/11/2018 3:23 PM, Rafael J. Wysocki wrote:
> > > > > > On Sunday, July 8, 2018 7:34:12 PM CEST Vivek Gautam wrote:
> > > > > > > From: Sricharan R <sricharan@xxxxxxxxxxxxxx>
> > > > > > >
> > > > > > > Finally add the device link between the master device and
> > > > > > > smmu, so that the smmu gets runtime enabled/disabled only when the
> > > > > > > master needs it. This is done from add_device callback which gets
> > > > > > > called once when the master is added to the smmu.
> > > > > > >
> > > > > > > Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx>
> > > > > > > Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> > > > > > > Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > > > > > > Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> > > > > > > Cc: Lukas Wunner <lukas@xxxxxxxxx>
> > > > > > > ---
> > > > > > >
> > > > > > >     - Change since v11
> > > > > > >       * Replaced DL_FLAG_AUTOREMOVE flag with
> > > > > > > DL_FLAG_AUTOREMOVE_SUPPLIER.
> > > > > > >
> > > > > > >     drivers/iommu/arm-smmu.c | 12 ++++++++++++
> > > > > > >     1 file changed, 12 insertions(+)
> > > > > > >
> > > > > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > > > > > > index 09265e206e2d..916cde4954d2 100644
> > > > > > > --- a/drivers/iommu/arm-smmu.c
> > > > > > > +++ b/drivers/iommu/arm-smmu.c
> > > > > > > @@ -1461,8 +1461,20 @@ static int arm_smmu_add_device(struct device
> > > > > > > *dev)
> > > > > > >           iommu_device_link(&smmu->iommu, dev);
> > > > > > >     +     if (pm_runtime_enabled(smmu->dev) &&
> > > > > > Why does the creation of the link depend on whether or not runtime PM
> > > > > > is enabled for the MMU device?
> > > > >
> > > > > The main purpose of this device link is to handle the runtime PM
> > > > > synchronization
> > > > > between the supplier (iommu) and consumer (client devices, such as
> > > > > GPU/display).
> > > > > Moreover, the runtime pm is conditionally enabled for smmu devices that
> > > > > support
> > > > > such [1].
> > > > Is there something you would like me to modify in this patch?
> > > Not really, as long as you are sure that it is correct. :-)
> > >
> > > You need to remember, however, that if you add system-wide PM
> > > callbacks to the driver, the ordering between them and the client
> > > device callbacks during system-wide suspend matters as well.  Don't
> > > you need the link the ensure the correct system-wide suspend ordering
> > > too?
> >
> > The fact that currently we handle clocks only through runtime pm callbacks,
> > would it be better to call runtime pm put/get in system-wide PM callbacks.
> > This would be same as i mentioned in the other thread.
> Well, my point is that there's no reason for system-wide suspend to
> depend directly on runtime PM (which can be effectively disabled by
> user space as mentioned for multiple times in this thread).
>
> It simply is not efficient to let the clock run while the system as a
> whole is sleeping (even if power/control has been set to "on" for this
> particular device) and it should not be too hard to prevent that from
> happening.  You may need an additional flag in the driver for that or
> similar, but it definitely should be doable.

Right, I will modify the things are required. Thanks again for pointing 
this out.

Best regards
Vivek

> Now, that's my advice and I'm not the maintainer of that code, so it
> is your call (as long as the maintainer agrees with it).
>
> Thanks,
> Rafael