Re: [PATCH v3 0/6] arm64: qcom: allow up to 4 lanes for the Type-C DisplayPort Altmode

[Neil Armstrong]

On 28/05/2025 18:56, Konrad Dybcio wrote:
> On 5/28/25 1:22 PM, Dmitry Baryshkov wrote:
> > On Wed, May 28, 2025 at 01:13:26PM +0200, Konrad Dybcio wrote:
> > > On 5/28/25 11:00 AM, Dmitry Baryshkov wrote:
> > > > On Wed, May 28, 2025 at 12:24:02AM +0200, Konrad Dybcio wrote:
> > > > > On 5/27/25 11:10 PM, Dmitry Baryshkov wrote:
> > > > > > On Tue, May 27, 2025 at 10:40:02PM +0200, Konrad Dybcio wrote:
> > > > > > > Register a typec mux in order to change the PHY mode on the Type-C
> > > > > > > mux events depending on the mode and the svid when in Altmode setup.
> > > > > > >
> > > > > > > The DisplayPort phy should be left enabled if is still powered on
> > > > > > > by the DRM DisplayPort controller, so bail out until the DisplayPort
> > > > > > > PHY is not powered off.
> > > > > >
> > > > > > This series doesn't seem to solve the USB side of a problem. When the
> > > > > > PHY is being switch to the 4-lane mode, USB controller looses PIPE
> > > > > > clock, so it needs to be switched to the USB-2 mode.
> > > > >
> > > > > I didn't find issues with that on X13s.. Not sure if it's related, but
> > > > > on the SL7, after plugging in a 4ln DP connection, I need to plug in
> > > > > the USB thumb drive twice for the first time (only in that sequence)
> > > >
> > > > Might be.
> > > >
> > > > > But there's nothing interesting in dmesg and the phy seems to be
> > > > > programmed with the same values on both the initial and the subsequent
> > > > > working plug-in
> > > >
> > > > Please try using a DP dongle with USB 2 passthrough (there are some).
> > > > Or just emulate this by enabling DP PHY / DP chain for plugged in USB3
> > > > devices. Would you be able to see the USB device on a bus?
> > >
> > > I only have a dongle with both display and usb that does 2ln dp
> > > (I tested 4ln dp on a type-c display that I don't think has a hub)
> > >
> > > USB3 - yes, USB2 - no (but it works after a replug)
> > >
> > > Are you talking about essentially doing qcom,select-utmi-as-pipe-clk
> > > at runtime?
> >
> > I think so.
>
> So after quite some time playing with that, I noticed that the USB2
> device was never actually kicked off the bus.. and works totally fine
> after connecting the display output (2ln DP)
>
> I was looking at dmesg, checking for discovery/disconnect messages,
> but the device was simply never disconnected (which makes sense given
> repurposing USB3 TX/RX lanes doesn't affect the D+/D- of USB2)
>
> I also read some docs and learnt that what we call
> qcom,select-utmi-as-pipe-clk is suppossed to be a debug feature
> and is unnecessary to set on USB2.0-only controllers
>
> The USB controller programming guide though doesn't talk about DP,
> but I'd expect that we may need to set that override for 4lnDP+USB2
> use cases (which I don't have a dongle for)

Yeah basically we need to:
1) power-off the USB3 PHY
2) switch to UTMI clock

In the following states:
- USB safe mode (USB2 lanes may still be connected)
- 4lanes DP mode
- DP-only mode

But for this, the dwc3 should also get USB-C events with an addition mode-switch property.
The flatten DWC3 node now allows that !

Neil

> Konrad