Re: [PATCH 1/2] dt-bindings: phy: mediatek: tphy: add a property for force-mode switch

[Chunfeng Yun (云春峰)]

On Mon, 2023-11-27 at 08:21 +0100, Krzysztof Kozlowski wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On 27/11/2023 08:09, Macpaul Lin wrote:
> > On 11/25/23 18:37, Krzysztof Kozlowski and Chunfeng Yun wrote:
> >> 
> >>
> >> External email : Please do not click links or open attachments
> until you 
> >> have verified the sender or the content.
> >>
> >> On 25/11/2023 02:23, Chunfeng Yun wrote:
> >>> Due to some old SoCs with shared t-phy only support force-mode
> switch, and
> >>> can't use compatible to distinguish between shared and non-shared 
> t-phy,
> >>> add a property to supported it.
> >>> But now prefer to use "mediatek,syscon-type" on new SoC as far as
> possible.
> >>>
> >>> Signed-off-by: Chunfeng Yun <chunfeng.yun@xxxxxxxxxxxx>
> >>> ---
> >>>  Documentation/devicetree/bindings/phy/mediatek,tphy.yaml | 6
> ++++++
> >>>  1 file changed, 6 insertions(+)
> >>>
> >>> diff --git
> a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> >>> index 2bb91542e984..eedba5b7025e 100644
> >>> --- a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> >>> +++ b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> >>> @@ -235,6 +235,12 @@ patternProperties:
> >>>            Specify the flag to enable BC1.2 if support it
> >>>          type: boolean
> >>>  
> >>> +      mediatek,force-mode:
> >>> +        description:
> >>> +          Use force mode to switch shared phy mode, perfer to
> use the bellow
> >>
> >> I still do not understand what is the "force mode" you want to
> use. What
> >> modes do you have? What are the characteristics of force mode?
> >>
> >> Also, please run spellcheck.
> >>
> >> Best regards,
> >> Krzysztof
> >>
> > 
> > Thanks!
> > 
> > 1. I've tested this patch and it could solve the clock unstable for
> > XHCI1 on mt8195 or mt8395 during system boot up or during
> > unload/reload the phy driver.
> > 
> > The error message has been listed as follows.
> > 
> > [   13.849936][   T72] xhci-mtk 11290000.usb: supply vbus not
> found, 
> > using dummy regulator
> > [   13.851300][   T72] xhci-mtk 11290000.usb: uwk - reg:0x400,
> version:104
> > [   13.852624][   T72] xhci-mtk 11290000.usb: xHCI Host Controller
> > [   13.853393][   T72] xhci-mtk 11290000.usb: new USB bus
> registered, 
> > assigned bus number 3
> > [   13.874490][   T72] xhci-mtk 11290000.usb: clocks are not stable
> (0x3d0f)
> > [   13.875369][   T72] xhci-mtk 11290000.usb: can't setup: -110
> > [   13.876091][   T72] xhci-mtk 11290000.usb: USB bus 3
> deregistered
> > [   13.877081][   T72] xhci-mtk: probe of 11290000.usb failed with
> error 
> > -110
> > 
> > 2. This is a fix patch to XHCI1 since MT8195 has been upstream.
> > Please add "Fixes:" tags and "Cc: stable@xxxxxxxxxx" to back ward
> > porting to previous stable trees.
> > 
> > For example, add
> > Fixes: 6b5ef194611e5 ("phy: mediatek: tphy: remove macros to
> prepare 
> > bitfield")
> > is suggested since the force-mode was missing in the previous
> > implementation which causes hardware function was abnormal.
> > However, add
> > Fixes: 33d18746fa514 ("phy: phy-mtk-tphy: use new io helpers to
> access 
> > register")
> > will be better since the USB support for mt8195 is already enabled
> in 
> > late 2021.
> > 
> > 3. How about we revise the description as follows for more
> precisely?
> > 
> > mediatek,force-mode:
> >    description:
> >      The force mode is used to manually switch the shared PHY mode
> >      between USB and PCIe. When force-mode is set, the USB 3.0 mode
> >      will be selected. This is typically required for older SoCs
> >      that do not automatically manage PHY mode switching.
> >      For newer SoCs that support it, it is preferable to use the
> >      "mediatek,syscon-type" property instead.
> >    type: boolean
> 
> Again, what is force-mode? 
Our DE describe this behavior as force-mode, as you see, the driver
power down controller and reset pipe to set the mode directly we want,
but usually the phy controller switch to the mode automatically
according to the external signal, e.g. trapping pin, efuse etc.

> It looks like you wrote bindings for the
> driver behavior. Bindings describe hardware, not how the driver
> should
> behave. The property might be reasonable, but you must describe here
> hardware characteristics/issue/etc.
> 
> Also, your driver change suggests this is compatible specific, so why
> it
> cannot be deduced from compatible?
that is because on the same SoC, some t-phy supported USB3 are shared
with PCIe, but others are not, use the SoC's compatible can not
distinguish them.
> 
> Best regards,
> Krzysztof
>