Re: [PATCH 1/3] dt-bindings: phy: mediatek: tphy: add support hardware version 3

[Chunfeng Yun <chunfeng.yun@mediatek.com>]

On Wed, 2021-06-16 at 17:28 -0600, Rob Herring wrote:
> On Fri, Jun 04, 2021 at 03:31:18PM +0800, Chunfeng Yun wrote:
> > The PHYA architecture is updated, and doesn't support slew rate
> > calibration anymore on 7nm or advanced process, add a new version
> > number to support it.
> > Note: the FreqMeter bank is not used but reserved.
> > 
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> > ---
> >  .../devicetree/bindings/phy/mediatek,tphy.yaml     | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > index b8a7651a3d9a..939c09296b5f 100644
> > --- a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > +++ b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > @@ -15,7 +15,7 @@ description: |
> >    controllers on MediaTek SoCs, includes USB2.0, USB3.0, PCIe and SATA.
> >  
> >    Layout differences of banks between T-PHY V1 (mt8173/mt2701) and
> > -  T-PHY V2 (mt2712) when works on USB mode:
> > +  T-PHY V2 (mt2712) / V3 (mt8195) when works on USB mode:
> >    -----------------------------------
> >    Version 1:
> >    port        offset    bank
> > @@ -34,7 +34,7 @@ description: |
> >    u2 port2    0x1800    U2PHY_COM
> >                ...
> >  
> > -  Version 2:
> > +  Version 2/3:
> >    port        offset    bank
> >    u2 port0    0x0000    MISC
> >                0x0100    FMREG
> > @@ -59,7 +59,8 @@ description: |
> >  
> >    SPLLC shared by u3 ports and FMREG shared by u2 ports on V1 are put back
> >    into each port; a new bank MISC for u2 ports and CHIP for u3 ports are
> > -  added on V2.
> > +  added on V2; the FMREG bank for slew rate calibration is not used anymore
> > +  and reserved on V3;
> >  
> >  properties:
> >    $nodename:
> > @@ -79,8 +80,11 @@ properties:
> >                - mediatek,mt2712-tphy
> >                - mediatek,mt7629-tphy
> >                - mediatek,mt8183-tphy
> > -              - mediatek,mt8195-tphy
> >            - const: mediatek,generic-tphy-v2
> 
> This doesn't look like a good change.
> 
> What happens if a DT has the above. It didn't work or didn't support new 
> features?
It does not affect function, but will waste some time to calibrate slew
rate on mt8195.

>  Please clarify in the commit the implications of changing 
> this. Changing a DT to 'mediatek,generic-tphy-v3' will break existing OS 
> if it was looking for v2.
On mt8195, it's backward compatible with hw v2, the unused FMREG bank is
reversed, but noop when W/R registers.
> 
> > +      - items:
> > +          - enum:
> > +              - mediatek,mt8195-tphy
> > +          - const: mediatek,generic-tphy-v3
> >        - const: mediatek,mt2701-u3phy
> >          deprecated: true
> >        - const: mediatek,mt2712-u3phy
> > @@ -91,7 +95,7 @@ properties:
> >      description:
> >        Register shared by multiple ports, exclude port's private register.
> >        It is needed for T-PHY V1, such as mt2701 and mt8173, but not for
> > -      T-PHY V2, such as mt2712.
> > +      T-PHY V2/V3, such as mt2712.
> >      maxItems: 1
> >  
> >    "#address-cells":
> > -- 
> > 2.18.0