Re: [PATCH v1 4/9] scsi: ufs: add option to change default UFS power management level

[Asutosh Das (asd)]

On 7/23/2018 8:06 PM, Rob Herring wrote:
> On Sun, Jul 22, 2018 at 9:20 PM Asutosh Das (asd)
> <asutoshd@xxxxxxxxxxxxxx> wrote:
> > On 7/12/2018 2:03 AM, Rob Herring wrote:
> > > On Fri, Jul 06, 2018 at 06:00:31PM +0530, Asutosh Das wrote:
> > > > From: Subhash Jadavani <subhashj@xxxxxxxxxxxxxx>
> > > >
> > > > UFS device and link can be put in multiple different low power modes hence
> > > > UFS driver supports multiple different low power modes. By default UFS
> > > > driver selects the default (optimal) low power mode (which gives moderate
> > > > power savings and have relatively less enter and exit latencies) but
> > > > we might have to tune this default power mode for different chipset
> > > > platforms to meet the low power requirements/goals. Hence this patch
> > > > adds option to change default UFS low power mode (level).
> > > >
> > > > Signed-off-by: Subhash Jadavani <subhashj@xxxxxxxxxxxxxx>
> > > > Signed-off-by: Venkat Gopalakrishnan <venkatg@xxxxxxxxxxxxxx>
> > > > Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx>
> > > > Signed-off-by: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
> > > > ---
> > > >    .../devicetree/bindings/ufs/ufshcd-pltfrm.txt      | 11 ++++++++
> > > >    drivers/scsi/ufs/ufshcd-pltfrm.c                   | 14 +++++++++++
> > > >    drivers/scsi/ufs/ufshcd.c                          | 29 +++++++++++++++-------
> > > >    drivers/scsi/ufs/ufshcd.h                          |  4 +--
> > > >    4 files changed, 47 insertions(+), 11 deletions(-)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > > index c39dfef..f564d9a 100644
> > > > --- a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > > +++ b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > > @@ -38,6 +38,15 @@ Optional properties:
> > > >                         defined or a value in the array is "0" then it is assumed
> > > >                         that the frequency is set by the parent clock or a
> > > >                         fixed rate clock source.
> > > > +- rpm-level         : UFS Runtime power management level. Following PM levels are supported:
> > > > +                      0 - Both UFS device and Link in active state (Highest power consumption)
> > > > +                      1 - UFS device in active state but Link in Hibern8 state
> > > > +                      2 - UFS device in Sleep state but Link in active state
> > > > +                      3 - UFS device in Sleep state and Link in hibern8 state (default PM level)
> > > > +                      4 - UFS device in Power-down state and Link in Hibern8 state
> > > > +                      5 - UFS device in Power-down state and Link in OFF state (Lowest power consumption)
> > > > +- spm-level         : UFS System power management level. Allowed PM levels are same as rpm-level.
> > >
> > > What's the default?
> > >
> > > I assume these are minimums? The OS can pick higher power states. This
> > > seems to be a bit Linux specific (as 'runtime PM' could be considered
> > > Linux specific). For every other device, we don't put this type of
> > > information in DT, but is user controlled.
> > I didn't completely understand your comment.
> > Do you not want these properties to be in DT file?
>
> Right, not if it is a user decision.
>
> > When you say user-controlled, do you mean control it through sysfs entries?
>
> Yes.
>
> > > So really, wouldn't 1
> > > property be sufficient for cases where a mode doesn't work due to
> > > some h/w limitation. Otherwise, it is an OS or user decision.
> > I didn't completely understand this. Could you please elaborate on your
> > intent here?
>
> The case that makes sense for this to be in DT is if there are h/w
> limitations that prevent some low power modes. In such a case, that
> limit is not likely specific to runtime PM or system suspend.
>
> > > >    -lanes-per-direction       : number of lanes available per direction - either 1 or 2.
> > > >                         Note that it is assume same number of lanes is used both
> > > >                         directions at once. If not specified, default is 2 lanes per direction.
> > > > @@ -66,4 +75,6 @@ Example:
> > > >               freq-table-hz = <100000000 200000000>, <0 0>, <0 0>;
> > > >               phys = <&ufsphy1>;
> > > >               phy-names = "ufsphy";
> > > > +            rpm-level = <3>;
> > >
> > > Why specified if 3 is the default?
> > Ah yes - that should be removed.
> > I'll remove it in v2.
> >
> > > > +            spm-level = <5>;
> > >
> > > These seem like sane defaults. When and why would you use some
> > > different?
> > I think each of the deeper sleep modes are associated with an increasing
> > wakeup latency. For e.g. '0' would have the highest power-consumption
> > and no resume latency at all as compared to '5'.
> > So depending on use-cases other modes may be chosen.
>
> The use-case can change in a running system. For example if you are
> plugged in, then you probably don't want to enter a lower power mode.
>
> Rob

Ok - Thanks.
I'm gonna make the following changes in v2:
1. Remove these entries from DT
2. Add support for these entries in sysfs.
3. Keep 3 as the default value for [rpm/spm]-levels

-asd

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