Re: [PATCH v3 1/5] dt-bindings: phy: qcom,sc8280xp-qmp-pcie-phy: Add support for glymur Gen5 x8 bifurcation mode

[Qiang Yu <qiang.yu@oss.qualcomm.com>]

On Fri, Apr 17, 2026 at 11:18:08AM +0200, Krzysztof Kozlowski wrote:
> On Wed, Apr 15, 2026 at 07:58:13PM -0700, Qiang Yu wrote:
> > On Wed, Apr 15, 2026 at 09:50:28AM +0200, Krzysztof Kozlowski wrote:
> > > On Sun, Apr 12, 2026 at 11:25:56PM -0700, Qiang Yu wrote:
> > > > The Glymur SoC has pcie3a and pcie3b PHYs that can operate in two modes:
> > > > 
> > > > 1. Independent 4-lane mode: Each PHY operates as a separate PCIe Gen5
> > > >    4-lane interface, compatible with qcom,glymur-qmp-gen5x4-pcie-phy
> > > > 2. Bifurcation mode (8-lane): pcie3a phy acts as leader and pcie3b phy as
> > > >    follower to form a single 8-lane PCIe Gen5 interface
> > > > 
> > > > In bifurcation mode, the hardware design requires controlling additional
> > > > resources beyond the standard pcie3a PHY configuration:
> > > > 
> > > > - pcie3b's aux_clk (phy_b_aux)
> > > > - pcie3b's phy_gdsc power domain
> > > > - pcie3b's bcr/nocsr reset
> > > > 
> > > > Add qcom,glymur-qmp-gen5x8-pcie-phy compatible string to document this
> > > > 8-lane bifurcation configuration.
> > > 
> > > Do you describe PCI3A or PCI3B or something combined PCI3?
> > 
> > I describe a single x8 PHY with resources from both the pcie3a and pcie3b
> > PHY blocks for x8 operation.
> > 
> > > 
> > > > 
> > > > The phy_b_aux clock is used as the 6th clock instead of pipediv2,
> > > > requiring the clock-names enum to be extended to support both
> > > > [phy_b_aux, pipediv2] options at index 5. This follows the existing
> > > > pattern used for [rchng, refgen] clocks at index 3.
> > > > 
> > > > Signed-off-by: Qiang Yu <qiang.yu@oss.qualcomm.com>
> > > > ---
> > > >  .../bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml   | 53 ++++++++++++++++++----
> > > >  1 file changed, 45 insertions(+), 8 deletions(-)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml b/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml
> > > > index 3a35120a77ec0ceb814a1cdcacff32fef32b4f7b..14eba5d705b1956c1bb00cc8c95171ed6488299b 100644
> > > > --- a/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml
> > > > +++ b/Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml
> > > > @@ -18,6 +18,7 @@ properties:
> > > >      enum:
> > > >        - qcom,glymur-qmp-gen4x2-pcie-phy
> > > >        - qcom,glymur-qmp-gen5x4-pcie-phy
> > > > +      - qcom,glymur-qmp-gen5x8-pcie-phy
> > > 
> > > That's the same device as 5x4, no? One device, one compatible and this
> > > suggests you will have three PCI phys in the DT - two 5x4 and one 5x8?
> > > 
> > 
> > It is not the same as the 5x4 PHY. In DT, we model three PHY nodes:
> > phy_3a (1x4), phy_3b (1x4), and a separate phy_1x8 node for x8 mode.
> 
> OK, that's what I wanted to hear. And that's what should not be done,
> 
> You should not have a separate node for the same hardware. First, DTC
> will give you a W=1 warning, although warning itself should be moved to
> W=2.
> 
> Second, the warning tells important story - same hardware is described
> twice.
> 
> You only need phy_3a and phy_3b, so only two in total.

We can keep only phy_3a and phy_3b, but still add new compatible
qcom,glymur-qmp-gen5x8-pcie-phy in binding, right?

For boards that support pcie3a(1x4) + pcie3b(1x4), DTS would be:

pcie3a_phy { compatible = "qcom,glymur-qmp-gen5x4-pcie-phy"; };
pcie3b_phy { compatible = "qcom,glymur-qmp-gen5x4-pcie-phy"; };

For boards that support 1x8, we would override pcie3a_phy with:

pcie3a_phy { compatible = "qcom,glymur-qmp-gen5x8-pcie-phy"; /* additional resources */ };
pcie3b_phy { compatible = "qcom,glymur-qmp-gen5x4-pcie-phy"; };

This still uses only two PHY nodes and DTC will not report warning.

- Qiang Yu
> 
> phy_3a could have resources of phy_3b OR could have a phandle to
> companion (follower) phy to fetch resources from it. I don't know yet
> which choice is better, though.
> 
> Best regards,
> Krzysztof
>