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

Laurent Pinchart
2026-04-25T23:48:49Z

On Sun, Apr 26, 2026 at 12:44:59AM +0300, Dmitry Baryshkov wrote:
> On Sat, Apr 25, 2026 at 01:10:02PM -0500, Dennis Gilmore wrote:
> > On Sat, Apr 25, 2026 at 9:24 AM Dmitry Baryshkov 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.
>
> I think it would be nice to mention:
> - In the commit for the bindings, that the device can be running
> uncontrolled or it can be attached over I2C, bindings describe the
> uncontrolled mode.
> - In this commit message, the same.
> - In the commit message for the board DT mention your findings about the
> board, mention soldering R9 or R17 (which one?) and R27.

Additionally, how are we going to handle boards where the device
operates in I2C mode ? Will we use a different compatible string (maybe
"lontium,lt8711uxd-i2c") ? If DT maintainers are fine with that, I have
no objection to this patch.

> > > > > Signed-off-by: Dennis Gilmore <dennis@ausil.us>
> > > > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@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