Re: [PATCH v2 1/2] dt-bindings: display/bridge: lt9211: Add drive-strength-microamp property

["Börge Strümpfel" <bstruempfel@data-modul.com>]

On Thu, May 14, 2026 at 05:26:03AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The values for `drive-strength-microamp` are scaled incorrectly by a factor of 100, violating the standard device tree unit suffix.
> --
> 

Thank you for your review

> commit ab265d46e886455894986f313701d72a9407a58e
> Author: Boerge Struempfel <bstruempfel@data-modul.com>
> 
> dt-bindings: display/bridge: lt9211: Add drive-strength-microamp property
> 
> This commit adds the drive-strength-microamp property to configure the
> LT9211 LVDS TX output driver current. It specifies sixteen discrete levels
> ranging from 12 to 36.
> 
> > diff --git a/Documentation/devicetree/bindings/display/bridge/lontium,lt9211.yaml b/Documentation/devicetree/bindings/display/bridge/lontium,lt9211.yaml
> > --- a/Documentation/devicetree/bindings/display/bridge/lontium,lt9211.yaml
> > +++ b/Documentation/devicetree/bindings/display/bridge/lontium,lt9211.yaml
> [ ... ]
> > +  drive-strength-microamp:
> > +    description:
> > +      LVDS TX output driver current. Sixteen discrete levels are supported,
> > +      corresponding to the following nominal values in microamps.
> > +    enum: [12, 14, 16, 17, 19, 20, 22, 23, 25, 27, 28, 30, 31, 33, 34, 36]
> 
> Are these values scaled incorrectly for a property ending in -microamp?
> 
> Properties with the -microamp suffix typically require values in true
> microamperes. A standard LVDS driver requires differential currents in the
> milliamp range, typically 1.25 mA to 3.59 mA, to generate a standard 350 mV
> swing over a 100-ohm termination.
> 
> Values from 12 to 36 microamps appear to be physically insufficient for LVDS
> signaling.
> 
> If the actual intended currents are 1.25 mA to 3.59 mA, shouldn't the enum
> values be 1250, 1406, 1562, up to 3594 to accurately reflect true
> microamperes?
> 

I double-checked the partial datasheet I was provided by Lontium. It
states for RG_MLTX_HSDRV_ISEL: "Port A/B mipi/lvds tx hstx current
select, 4'b0000 = 12.5 µA, 4'b1111 = 35.9735 µA, step = 1.5625 µA".
Those are the values I took as a reference for this commit. However, I
did not measure them myself and this might be a mistake in the datasheet
or there might be some amplification happening after, which is not
described in the part of the datasheet I got.

Maybe someone else has more insight into this?

In the meantime, I will try to follow up with our hardware team and try
to contact Lontium to clarify where this discrepancy between the
datasheet values and the expected LVDS output current range comes from.

> -- 
> Sashiko AI review   https://sashiko.dev/#/patchset/20260513133127.376458-1-bstruempfel@data-modul.com?part=1

-- 
Best regards,
Börge Strümpfel

DATA MODUL AG
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