linux-kernel - Re: [PATCH v3 1/4] dt-bindings: display: mediatek: add property to control mipi tx drive current

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Message-ID: <1585638593.31955.5.camel@mszsdaap41>
Date:   Tue, 31 Mar 2020 15:09:53 +0800
From:   Jitao Shi <jitao.shi@...iatek.com>
To:     Rob Herring <robh@...nel.org>
CC:     Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <yingjoe.chen@...iatek.com>,
        <eddie.huang@...iatek.com>, <cawa.cheng@...iatek.com>,
        <bibby.hsieh@...iatek.com>, <ck.hu@...iatek.com>,
        <stonea168@....com>, <huijuan.xie@...iatek.com>
Subject: Re: [PATCH v3 1/4] dt-bindings: display: mediatek: add property to
 control mipi tx drive current


On Mon, 2020-03-23 at 16:00 -0600, Rob Herring wrote:
> On Wed, Mar 11, 2020 at 03:40:29PM +0800, Jitao Shi wrote:
> > Add a property to control mipi tx drive current:
> > "drive-strength-microamp"
> > 
> > Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
> > ---
> >  .../devicetree/bindings/display/mediatek/mediatek,dsi.txt     | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/display/mediatek/mediatek,dsi.txt b/Documentation/devicetree/bindings/display/mediatek/mediatek,dsi.txt
> > index a19a6cc375ed..d501f9ff4b1f 100644
> > --- a/Documentation/devicetree/bindings/display/mediatek/mediatek,dsi.txt
> > +++ b/Documentation/devicetree/bindings/display/mediatek/mediatek,dsi.txt
> > @@ -33,6 +33,9 @@ Required properties:
> >  - #clock-cells: must be <0>;
> >  - #phy-cells: must be <0>.
> >  
> > +Optional properties:
> > +- drive-strength-microamp: adjust driving current, should be 1 ~ 0xF
> 
> TBC, 1-0xf is in units of microamps? So a max drive strength of 15uA? 
> Seems a bit low.
> 

The minimum amp is 3000 macroamps,  step is 200macroamps.
So the drive current is 3000 + 200 * drive-strength-microamp amps.

I will update "drive-strength-microamp" define next version.

BR
Jitao
> > +
> >  Example:
> >  
> >  mipi_tx0: mipi-dphy@...15000 {
> > @@ -42,6 +45,7 @@ mipi_tx0: mipi-dphy@...15000 {
> >  	clock-output-names = "mipi_tx0_pll";
> >  	#clock-cells = <0>;
> >  	#phy-cells = <0>;
> > +	drive-strength-microamp = <0x8>;
> >  };
> >  
> >  dsi0: dsi@...1b000 {
> > -- 
> > 2.21.0