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

Mahadevan P
2026-04-22T12:31:13Z

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@oss.qualcomm.com>
>> ---
>> 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