Re: [PATCH 3/8] phy: qcom: qmp-usbc: Add DP phy mode support on QCS615

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On Wed, Dec 11, 2024 at 08:46:16AM +0800, Xiangxu Yin wrote:
> 
> 
> On 12/10/2024 11:09 PM, Dmitry Baryshkov wrote:
> > On Thu, Dec 05, 2024 at 08:31:24PM +0200, Dmitry Baryshkov wrote:
> >> On Thu, Dec 05, 2024 at 09:26:47PM +0800, Xiangxu Yin wrote:
> >>>
> >>>
> >>> On 11/29/2024 10:33 PM, Dmitry Baryshkov wrote:
> >>>> On Fri, 29 Nov 2024 at 09:59, Xiangxu Yin <quic_xiangxuy@xxxxxxxxxxx> wrote:
> >>>>>
> >>>>> Extended DP support for QCS615 USB or DP phy. Differentiated between
> >>>>> USBC and DP PHY using the match table’s type, dynamically generating
> >>>>> different types of cfg and layout attributes during initialization based
> >>>>> on this type. Static variables are stored in cfg, while parsed values
> >>>>> are organized into the layout structure.
> >>>>
> >>>> We didn't have an understanding / conclusion whether
> >>>> qcom,usb-ssphy-qmp-usb3-or-dp PHYs are actually a single device / PHY
> >>>> or two PHYs being placed next to each other. Could you please start
> >>>> your commit message by explaining it? Or even better, make that a part
> >>>> of the cover letter for a new series touching just the USBC PHY
> >>>> driver. DP changes don't have anything in common with the PHY changes,
> >>>> so you can split the series into two.
> >>>>
> >>> Before implement DP extension, we have discussed with abhinav and krishna about whether use combo, usbc or separate phy.
> >>
> >> What is "DP extension"?
> >>
> I'm sorry confusion casued by my description. It's means extend DP implemnt for USBC phy driver.
> >>>
> >>> We identified that DP and USB share some common controls for phy_mode and orientation.
> >>> Specifically, 'TCSR_USB3_0_DP_PHYMODE' controls who must use the lanes - USB or DP,
> >>> while PERIPH_SS_USB0_USB3PHY_PCS_MISC_TYPEC_CTRL controls the orientation.
> >>> It would be more efficient for a single driver to manage these controls. 
> >>
> >> The question is about the hardware, not about the driver.
> >>
> >>> Additionally, this PHY does not support Alt Mode, and the two control registers are located in separate address spaces. 
> >>> Therefore, even though the orientation for DP on this platform is always normal and connected to the video output board, 
> >>> we still decided to base it on the USBC extension.
> >>
> >> Could you please clarify, do usb3-or-dp PHYs support DP-over-USB-C? I
> >> thought that usbc-or-dp platforms support that, but they don't
> >> support DP+USB pin configuration. Note, the question is broader than
> >> just QCS615, it covers the PHY type itself.
> >>
> >> Also, is TCSR configuration read/write or read-only? Are we supposed to
> >> set the register from OS or are we supposed to read it and thus detemine
> >> the PHY mode?
> > 
> > Any updates on these two topics?
> > 
> Still confirming detail info with HW & design team.
> I’ll update the information that has been confirmed so far.
> This phy support DP-over-USB-C,but it's not support alt-mode which 2 lane work for DP, other 2 lane work for USB.
> TCSR phy mode is read/write reg and we can read for determine phy mode.

Ok, thanks for the explanation. From my point of view:

- Implement the DP PHY to be a part of the same driver. Each device
  supported by the usbc driver should get both PHYs.

- Make sure not to break the ABI: #phy-cells = <0> should still work and
  return USB PHY, keeping backwards compatibility. Newer devices or
  upgraded DT for old devices should return USB PHY for <... 0> and DP
  PHY for <... 1>.

- I'm not shure how to handle the USB and DP coexistence, especially in
  your case of the USB-or-DP PHY.

-- 
With best wishes
Dmitry