linux-kernel - Re: [PATCH V2 2/3] dt-bindings: mmc: sdhci-msm: Add entries for passing load values

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Date:   Fri, 21 Sep 2018 13:06:54 -0700
From:   Evan Green <evgreen@...omium.org>
To:     vbadigan@...eaurora.org
Cc:     adrian.hunter@...el.com, Ulf Hansson <ulf.hansson@...aro.org>,
        robh+dt@...nel.org, linux-mmc@...r.kernel.org,
        asutoshd@...eaurora.org, riteshh@...eaurora.org,
        stummala@...eaurora.org, sayali <sayalil@...eaurora.org>,
        Doug Anderson <dianders@...gle.com>, vviswana@...eaurora.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/3] dt-bindings: mmc: sdhci-msm: Add entries for
 passing load values

On Fri, Sep 21, 2018 at 3:32 AM Veerabhadrarao Badiganti
<vbadigan@...eaurora.org> wrote:
>
> Hi Evan,
>
>
> On 9/21/2018 5:45 AM, Evan Green wrote:
> > On Wed, Sep 19, 2018 at 11:24 PM Veerabhadrarao Badiganti
> > <vbadigan@...eaurora.org> wrote:
> >> From: Vijay Viswanath <vviswana@...eaurora.org>
> >>
> >> The load a particular sdhc controller should request from a regulator
> >> is device specific and hence each device should individually vote for
> >> the required load.
> >>
> >> Signed-off-by: Vijay Viswanath <vviswana@...eaurora.org>
> >> Signed-off-by: Veerabhadrarao Badiganti <vbadigan@...eaurora.org>
> >> ---
> >>   Documentation/devicetree/bindings/mmc/sdhci-msm.txt | 6 ++++++
> >>   1 file changed, 6 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> >> index 502b3b8..3720385 100644
> >> --- a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> >> +++ b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> >> @@ -26,6 +26,11 @@ Required properties:
> >>          "cal"   - reference clock for RCLK delay calibration (optional)
> >>          "sleep" - sleep clock for RCLK delay calibration (optional)
> >>
> >> +Optional properties:
> >> +- qcom,<supply>-current-level-microamp - specifies load levels for supply during BUS_ON and
> >> +                                       BUS_OFF states in power irq. Should be specified in
> >> +                                       pairs (lpm, hpm), for BUS_OFF and BUS_ON respectively.
> >> +                                       Units uA.
> >>   Example:
> >>
> >>          sdhc_1: sdhci@...24900 {
> >> @@ -37,6 +42,7 @@ Example:
> >>
> >>                  vmmc-supply = <&pm8941_l20>;
> >>                  vqmmc-supply = <&pm8941_s3>;
> >> +               qcom,vqmmc-current-level-microamp = <200 22000>;
> >>
> >>                  pinctrl-names = "default";
> >>                  pinctrl-0 = <&sdc1_clk &sdc1_cmd &sdc1_data>;
> >> --
> >> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
> >>
> > Aren't the regulator load levels pretty coarse? Would it be safe to
> > say that pretty much all sd/mmc devices need the high powered mode, or
> > are there really some devices that can get by with LPM all the time?
> > -Evan
> The load levels here are min and max supported by the regulator. To
> cover all devices
> we do set it to max load. We can't make any assumptions on this,  as
> peak current may vary
> from device to device.

Hi Veera,
If it were up to me, I would just assume all devices need high power
mode for BUS_ON and low power mode for BUS_OFF, and skip adding this
binding until you actually came up with a device that needed lower
power mode for BUS_ON, or high power mode for BUS_OFF (when would that
be, anyway?) Are there any actual use cases you've seen that need
different values in here?
-Evan