[PATCH v8 3/6] drm/bridge: simple: Add the Lontium LT8711UXD DP-to-HDMI bridge

[Dennis Gilmore]

On Sat, Apr 25, 2026 at 9:24 AM Dmitry Baryshkov
<dmitry.baryshkov at oss.qualcomm.com> wrote:
>
> On Sat, Apr 25, 2026 at 02:28:44PM +0300, Laurent Pinchart wrote:
> > Hi Dennis,
> >
> > Thank you for the patch.
> >
> > On Fri, Apr 24, 2026 at 10:10:08PM -0500, Dennis Gilmore wrote:
> > > The Lontium LT8711UXD is a high performance two lane Type-C/DP1.4
> > > to HDMI2.0 converter, designed to connect a USB Type-C source or
> > > a DP1.4 source to an HDMI2.0 sink.
> >
> > As far as I can tell, the LT8711UXD has an I2C control interface.
> > Shouldn't it be an I2C device ?
>
> From the datasheet:
>
> The device is capable of automatic operation which is
> enabled by an integrated microprocessor that uses an
> embedded SPI flash for firmware storage. System control
> is also available through the use of a dedicated
> configuration I2C slave interface.
>
> My guess was that it can either be an I2C device or it can function as a
> simple platdev with no I2C controls. Please correct me if my
> understanding was wrong.
>
> But now looking at the schematics, it seems to be connected to I2C6.
> Which means that it should be desribed (and bound) as such.

Hi Dmitry and Laurent,

While the schematic shows that it can use I2C and has been wired up,
it also shows that both MODE_SEL and I2C_ADDR have unpopulated 10k
resistors; as a result, MODE_SEL is connected directly to GND, putting
the bridge in autonomous mode. I confirmed this by running `i2cdetect
-r -y 6`, with the only device on the bus being the HYM8563 RTC at
0x51. Without reworking the board, the device is not directly
controllable and just runs autonomously.

Dennis

> >
> > > Signed-off-by: Dennis Gilmore <dennis at ausil.us>
> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at oss.qualcomm.com>
> > > ---
> > >  drivers/gpu/drm/bridge/simple-bridge.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/bridge/simple-bridge.c b/drivers/gpu/drm/bridge/simple-bridge.c
> > > index 8aa31ca3c72d..42c1f3d5ba0c 100644
> > > --- a/drivers/gpu/drm/bridge/simple-bridge.c
> > > +++ b/drivers/gpu/drm/bridge/simple-bridge.c
> > > @@ -270,6 +270,11 @@ static const struct of_device_id simple_bridge_match[] = {
> > >             .data = &(const struct simple_bridge_info) {
> > >                     .connector_type = DRM_MODE_CONNECTOR_HDMIA,
> > >             },
> > > +   }, {
> > > +           .compatible = "lontium,lt8711uxd",
> > > +           .data = &(const struct simple_bridge_info) {
> > > +                   .connector_type = DRM_MODE_CONNECTOR_HDMIA,
> > > +           },
> > >     }, {
> > >             .compatible = "parade,ps185hdm",
> > >             .data = &(const struct simple_bridge_info) {
> >
> > --
> > Regards,
> >
> > Laurent Pinchart
>
> --
> With best wishes
> Dmitry