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

[Mahadevan P <mahadevan.p@oss.qualcomm.com>]

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