Re: [PATCH 3/5] phy: qualcomm: qmp-combo: Add preliminary USB4 support

[Konrad Dybcio]

On 5/18/26 5:38 PM, Dmitry Baryshkov wrote:
> On Mon, May 18, 2026 at 04:15:16PM +0200, Konrad Dybcio wrote:
>> On 5/18/26 3:57 PM, Dmitry Baryshkov wrote:
>>> On Mon, May 18, 2026 at 12:29:50PM +0200, Konrad Dybcio wrote:
>>>> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
>>>>
>>>> Some Combo PHYs (so far only on SC8280XP, X1E80100 and Glymur), come in
>>>> a flavor called USB43DP, which as the name implies, features USB4, USB3
>>>> and DP signal processing capabilities. In that architecture, USB3 and
>>>> USB4 PHYs share the same USB_PLL while featuring separate logic spaces.
>>>> The DP part is roughly the same as on the instances without USB4.
>>>>
>>>> The USB4 and USB3/DP operation modes of the PHY are mutually exclusive.
>>>> Only one USB protocol (and flavor of pipe clock) can be active at a
>>>> given moment (not to be confused with USB3 not being able to be
>>>> tunneled as USB4 packets - that of course remains possible).
>>>> The DP PLL is still used for clocking tunneled DP links. It may be
>>>> turned off to save power when no tunnels are active, but that's left as
>>>> a TODO item for now.
>>>>
>>>> Due to the nature of USB4, the Type-C handling happens entirely inside
>>>> the Host Router, and as such the QMPPHY's mux_set() function is
>>>> nullified for the period when USB4 PHY remains active. This is strictly
>>>> necessary, as the Host Router driver is going to excercise manual
>>>> control over the USB4 PHY's power state, which is needed by the suspend
>>>> and resume flows. Failure to control that synchronously with other
>>>> parts of the code results in a SoC crash by unlocked access.
>>>>
>>>> Because of that, a new struct phy is spawned to expose the USB4 mode,
>>>> along with a .set_mode callback to allow toggling between USB4 and TBT3
>>>> submodes.
>>>>
>>>> Thunderbolt 3, having a number of differences vs USB4, requires a
>>>> couple specific overrides, pertaining to electrical characteristics,
>>>> which are easily accommodated for.
>>>>
>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
>>>> ---
>>>>  drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 392 ++++++++++++++++++++++++------
>>>>  1 file changed, 322 insertions(+), 70 deletions(-)
>>>>
>>>
>>> Overall it looks good. The major question (after looking at TODOs), do
>>> we need a separate submode for USB+DP / TBT+DP?
>>
>> The problem space is as follows:
>>
>> After a TBT (collectively TBT3+ and USB4) link has been established and
>> we have a link partner, we may (based on the HW capabilities and user
>> config, such as kernel params but not only) start or stop a DP tunnel at
>> runtime. On Qualcomm hardware, the PHY is kept in USB4 mode and its DP
>> AUX lines are not used (instead, the encapsulated DP AUX packets are r/w
>> entirely within the USB4 subsystem via a pair of FIFOs that Linux sees
>> as a separate DP AUX host)
> 
> So far so good. But I still don't grok if having a DP-over-USB4 is a
> separate submode or not. I.e. I see code (and TODOs) to detect and
> handle DP going on and off. Would it be better if we specify that
> explicitly?

I really don't want to end up in a situation like we have with:

$ rg _USB include/linux/phy/phy.h
29:     PHY_MODE_USB_HOST,
30:     PHY_MODE_USB_HOST_LS,
31:     PHY_MODE_USB_HOST_FS,
32:     PHY_MODE_USB_HOST_HS,
33:     PHY_MODE_USB_HOST_SS,
34:     PHY_MODE_USB_DEVICE,
35:     PHY_MODE_USB_DEVICE_LS,
36:     PHY_MODE_USB_DEVICE_FS,
37:     PHY_MODE_USB_DEVICE_HS,
38:     PHY_MODE_USB_DEVICE_SS,
39:     PHY_MODE_USB_OTG,

>> Then, on hamoa/glymur specifically, any of the 3 USB4-capable DP hosts
>> can be muxed to either of the 2 DPIN ports on any of the 3 USB4 routers
>> (and each of these routers is hardwired to one of the PHYs).
>>
>> To underline, we have 3 DP producers and 6 consumers. If there's e.g. a
>> super high-res display at one of the physical ports, or a long
>> daisy-chain, we may need to use 2 DPTXes to service 1 receptacle. Then,
>> we would only need one of the PHYs (associated with the router that's
>> wired to that port) to provide a DP clock.
>>
>> This, along with the normal (logical or physical) present/absent status
>> can change at runtime. My plan is to use phy_set_opts(dp_tunelling=true)
>> or something along those lines to toggle that bit as necessary
> 
> I don't see phy_set_opts(). So maybe a submode then...

Sorry, I misremembered the name. The function is phy_configure(), and it
takes a union phy_configure_opts, hence the confusion

Konrad