Re: [PATCH v2 0/3] arm64: dts: qcom: kodiak: Enable 4-lane DP via QMP Combo PHY

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 6/22/26 12:11 AM, Doug Anderson wrote:
> Hi,
> 
> On Fri, Jun 19, 2026 at 8:34 AM Konrad Dybcio
> <konrad.dybcio@oss.qualcomm.com> wrote:

[...]


>>>
>>> Are you sure that herobrine has 4 lanes routed on the PCB?
>>
>> +Doug any chance you still have schematics for that old boy?
>>
>> Bjorn, perhaps we could switch to a model where we define the max
>> capabilities (i.e. 4-lane 8.1 GHz link) in the SoC DTs and only limit
>> them as necessary? Not meeting these is borderline a board defect anyway
> 
> Bleh, I'd forgotten what a pain it was to look at herobrine schematics
> with the whole qcard "abstraction".
> 
> My memory and a quick glance at schematics makes me say that herobrine
> only has 2 lanes of DP. The problem is that this SoC really wasn't
> designed with a laptop in mind. I seem to remember there only being
> one USB 3 port and it is muxed with two of the DP lanes (since the SoC
> is designed to drive a single Type-C port). In order to support all of
> the ports that a laptop should have, you pretty much need to feed that
> one USB 3 port into a USB hub and hardcode the DP to always use two
> lanes.
> 
> The two DP lanes then go to a mux where they can be routed either
> towards the left Type C port or the right Type C port.
> 
> In terms of whether we can support the 8.1 GHz link speed, I remember
> much debate during the project, but I don't recall all the details. I
> think the discussion was that we were supposed to support the higher
> speeds, but we had to disable them because they weren't working. From
> my fuzzy memory, it was unclear whether the problem was known to be
> hardware or software related. I can try to dig deeper if it's
> relevant.

If anyone still has herobrine easily accessible, I guess a smoke test
with a high res display and this:

diff --git a/arch/arm64/boot/dts/qcom/sc7280-herobrine.dtsi b/arch/arm64/boot/dts/qcom/sc7280-herobrine.dtsi
index 5c5e4f1dd221..a39e418fdabb 100644
--- a/arch/arm64/boot/dts/qcom/sc7280-herobrine.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7280-herobrine.dtsi
@@ -464,7 +464,7 @@ &mdss_dp {
 
 &mdss_dp_out {
        data-lanes = <0 1>;
-       link-frequencies = /bits/ 64 <1620000000 2700000000 5400000000>;
+       link-frequencies = /bits/ 64 <1620000000 2700000000 5400000000 8100000000>;
 };
 
 /* NVMe drive, enabled on a per-board basis */

would be the quickest way to confirm that. Although we can just leave
it as-is if it's problematic.. I think you said there's some folks that
still use it a couple years ago

Konrad