Re: [PATCH] arm64: dts: qcom: qcs6490-rb3gen2: Enable 4-lane DisplayPort Alt Mode

[Mahadevan P]

On 4/22/2026 4:19 PM, Konrad Dybcio wrote:
> On 4/20/26 12:00 PM, Mahadevan P wrote:
> > Add the mode-switch property to the QMP combo PHY so that mode-switch
> > events are routed to it, allowing the PHY to enter DisplayPort Alternate
> > Mode. Expand the DP data-lanes assignment from two to four lanes to make
> > use of the full link bandwidth available in this configuration.
> >
> > Signed-off-by: Mahadevan P <mahadevan.p@xxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > index e393ccf1884a..0c180e49816f 100644
> > --- a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > +++ b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > @@ -789,7 +789,7 @@ &mdss_dp {
> >   };
> >   
> >   &mdss_dp_out {
> > -	data-lanes = <0 1>;
> > +	data-lanes = <0 1 2 3>;
> >   	remote-endpoint = <&usb_dp_qmpphy_dp_in>;
>
> There was an issue with this on a similar kodiak-iot board:
>
> https://lore.kernel.org/linux-arm-msm/zjmf27y5i6ypba3nvsxxceuxn6yogp46lmtrjua37qa4ibrleq@4qv5s2wirgdh/
>
> Have you confirmed (through debugfs) that 4 lanes are in use when
> running this on r3g2?

yes
root@rb3gen2-core-kit:/sys/kernel/debug/dri/0/DP-1# cat  dp_debug

        name = msm_dp

        drm_dp_link

                rate = 540000

                num_lanes = 4

                capabilities = 1

        dp_panel_info:

                active = 3840x2160

                back_porch = 80x54

                front_porch = 48x3

                sync_width = 32x5

                active_low = 0x0

                h_skew = 0

                refresh rate = 60

                pixel clock khz = 533250

                bpp = 30

        dp_link:

                test_requested = 128

                num_lanes = 4

                bw_code = 20

                lclk = 540000000

                v_level = 2

                p_level = 0


> >   };
> >   
> > @@ -1391,6 +1391,7 @@ &usb_1_qmpphy {
> >   	vdda-phy-supply = <&vreg_l6b_1p2>;
> >   	vdda-pll-supply = <&vreg_l1b_0p912>;
> >   
> > +	mode-switch;
>
> This should be moved to kodiak.dtsi
sure
> Konrad