Re: [PATCH] arm64: dts: apq8096-db820c: Increase load on l21 for SDCARD

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 11 Oct 05:55 PDT 2019, Loic Poulain wrote:

> Hi Andy, Rob,
> 
> Could any of you take this patch?
> 

I've applied the patch now.

Thanks,
Bjorn

> On Thu, 13 Dec 2018 at 20:14, Doug Anderson <dianders@chromium.org> wrote:
> >
> > Hi,
> >
> > On Thu, Dec 13, 2018 at 6:46 AM Jeffrey Hugo <jhugo@codeaurora.org> wrote:
> > >
> > > On 12/13/2018 12:55 AM, Loic Poulain wrote:
> > > > Hi Jeffrey,
> > > >
> > > >
> > > > On Wed, 12 Dec 2018 at 18:23, Jeffrey Hugo <jhugo@codeaurora.org
> > > > <mailto:jhugo@codeaurora.org>> wrote:
> > > >
> > > >     On 12/12/2018 10:13 AM, Loic Poulain wrote:
> > > >      > In the same way as for msm8974-hammerhead, l21 load, used for SDCARD
> > > >      > VMMC, needs to be increased in order to prevent any voltage drop
> > > >     issues
> > > >      > (due to limited current) happening with some SDCARDS or during
> > > >     specific
> > > >      > operations (e.g. write).
> > > >      >
> > > >      > Fixes: 660a9763c6a9 (arm64: dts: qcom: db820c: Add pm8994
> > > >     regulator node)
> > > >      > Signed-off-by: Loic Poulain <loic.poulain@linaro.org
> > > >     <mailto:loic.poulain@linaro.org>>
> > > >      > ---
> > > >      >   arch/arm64/boot/dts/qcom/apq8096-db820c.dtsi | 2 ++
> > > >      >   1 file changed, 2 insertions(+)
> > > >      >
> > > >      > diff --git a/arch/arm64/boot/dts/qcom/apq8096-db820c.dtsi
> > > >     b/arch/arm64/boot/dts/qcom/apq8096-db820c.dtsi
> > > >      > index 104cad9..c15e2c0 100644
> > > >      > --- a/arch/arm64/boot/dts/qcom/apq8096-db820c.dtsi
> > > >      > +++ b/arch/arm64/boot/dts/qcom/apq8096-db820c.dtsi
> > > >      > @@ -634,6 +634,8 @@
> > > >      >                               l21 {
> > > >      >                                       regulator-min-microvolt =
> > > >     <2950000>;
> > > >      >                                       regulator-max-microvolt =
> > > >     <2950000>;
> > > >      > +                                     regulator-allow-set-load;
> > > >      > +                                     regulator-system-load =
> > > >     <200000>;
> > > >      >                               };
> > > >      >                               l22 {
> > > >      >                                       regulator-min-microvolt =
> > > >     <3300000>;
> > > >      >
> > > >
> > > >     I'm curious, why not update sdhci-msm to set the load on the regulator?
> > > >
> > > >
> > > > Yes you're right, and I saw that there is ongoing work:
> > > > https://patchwork.kernel.org/patch/10630731/
> > > >
> > > > Howerver I thought this change would be a quicker fix and easier to
> > > > backport in stable trees.
> > > > I assume all the device-tree vmmc loads will be removed at some point
> > > > when driven from sdhci.
> > > >
> > >
> > > I hadn't seen that.  Ok, seems good to me.
> >
> > NOTE: I'm personally not convinced that adding the "set_load" calls
> > into the SDHCI driver actually makes any sense.  I believe it adds
> > complexity for no benefit.  The only time you ever need to should ever
> > be fiddling with "set_load" calls is if the rail you're controlling
> > has some hope of being able to run at a lower power mode.  If there's
> > no hope of it being at a lower power mode then the constraints on the
> > rail should just force it to high power mode and be done with it.  The
> > patch here (using regulator-system-load) is one way to force it to a
> > high power mode and seems fine, but there are other ways.  See a
> > previous discussion [1].
> >
> > NOTE: IIRC the "ongoing work" patch you pointed at always sets the
> > load to a fixed level to turn it to "high power mode" when the
> > regulator is turned on and undoes that set_load when the regulator is
> > turned off.  That's no longer needed as of commit 5451781dadf8
> > ("regulator: core: Only count load for enabled consumers").  If
> > someone comes up with a case where it's useful to keep the SD card
> > rail turned on but in "low power mode" _then_ we should actually
> > consider adding set_load to the SD card driver.
> >
> > [1] https://lkml.kernel.org/r/CAD=FV=V4WFYoKLQ72pico4HCGgLDTae7xougivv6VWOSoPhLpg@mail.gmail.com
> >
> > -Doug