linux-kernel - RE: [v2 1/3] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

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Date:   Wed, 12 Jan 2022 15:17:06 +0000
From:   Rajeev Nandan <RAJEEVNY@....qualcomm.com>
To:     Rob Herring <robh@...nel.org>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>
CC:     quic_rajeevny <quic_rajeevny@...cinc.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sean@...rly.run" <sean@...rly.run>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        quic_mkrishn <quic_mkrishn@...cinc.com>,
        "jonathan@...ek.ca" <jonathan@...ek.ca>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "swboyd@...omium.org" <swboyd@...omium.org>
Subject: RE: [v2 1/3] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

Hi Dmitry, Rob,

Thanks for the review.
> 
> On Mon, Jan 10, 2022 at 05:06:03PM +0300, Dmitry Baryshkov wrote:
> > On Mon, 10 Jan 2022 at 15:56, Rajeev Nandan
> <quic_rajeevny@...cinc.com> wrote:
> > >
> > > In most cases, the default values of DSI PHY tuning registers should
> > > be sufficient as they are fully optimized. However, in some cases
> > > where extreme board parasitics cause the eye shape to degrade, the
> > > override bits can be used to improve the signal quality.
> > >
> > > The general guidelines for DSI PHY tuning include:
> > > - High and moderate data rates may benefit from the drive strength and
> > >   drive level tuning.
> > > - Drive strength tuning will affect the output impedance and may be used
> > >   for matching optimization.
> > > - Drive level tuning will affect the output levels without affecting the
> > >   impedance.
> > >
> > > The clock and data lanes have a calibration circuitry feature. The
> > > drive strength tuning can be done by adjusting rescode offset for
> > > hstop/hsbot, and the drive level tuning can be done by adjusting the
> > > LDO output level for the HSTX drive.
> > >
> > > Signed-off-by: Rajeev Nandan <quic_rajeevny@...cinc.com>
> > > ---
> > >
> > > Changes in v2:
> > >  - More details in the commit text (Stephen Boyd)
> > >  - Use human understandable values (Stephen Boyd, Dmitry Baryshkov)
> > >  - Do not take values that are going to be unused (Dmitry Baryshkov)
> > >
> > >  .../bindings/display/msm/dsi-phy-10nm.yaml         | 33
> ++++++++++++++++++++++
> > >  1 file changed, 33 insertions(+)
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> > > b/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> > > index 4399715..d0eb8f6 100644
> > > ---
> > > a/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> > > +++ b/Documentation/devicetree/bindings/display/msm/dsi-phy-
> 10nm.yam
> > > +++ l
> > > @@ -35,6 +35,35 @@ properties:
> > >        Connected to DSI0_MIPI_DSI_PLL_VDDA0P9 pin for sc7180 target and
> > >        connected to VDDA_MIPI_DSI_0_PLL_0P9 pin for sdm845 target
> >
> > Generic note:
> > I think these properties should be prefixed with "qcom," prefix.
Sure, I will update in next version along with removing encoding for phy-drive-ldo-level property.

> >
> > >
> > > +  phy-rescode-offset-top:
> > > +    $ref: /schemas/types.yaml#/definitions/uint8-array
> > > +    minItems: 5
> > > +    maxItems: 5
> > > +    description:
> > > +      Integer array of offset for pull-up legs rescode for all five lanes.
> > > +      To offset the drive strength from the calibrated value in an increasing
> > > +      or decreasing manner, use 6 bit two’s complement values.
> >
> > dtc should support negative values, google hints that <(-2)> should work.
This format is working.
> 
> Yes, but the schema checks don't check negative values correctly yet. So you
> can use 'int8-array', but just don't use negative values in the examples. I'm
> working on changes that will fix this issue.
> 
> What does 6-bit mean? 0x3f is negative? Just sign extend the values and
> specify the valid range instead:
> 
> minimum: -32
> maximum: 31
Yes, Rob. 0x3f is negative value (-1) in 6-bit two's complement.
I will implement your suggestion in the next patch version.

> 
> Rob

Thanks,
Rajeev