linux-kernel - Re: [PATCH v3 1/2] dt-bindings: phy: qcom,sc8280xp-qmp-pcie-phy: Document the X1E80100 QMP PCIe PHY Gen4 x4

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Message-ID: <CAA8EJpqD1XYbw35oxP4hWutbGs8nRTSwOsBAJcYGos8FBbAHew@mail.gmail.com>
Date: Fri, 30 Aug 2024 18:02:34 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Abel Vesa <abel.vesa@...aro.org>, Vinod Koul <vkoul@...nel.org>, 
	Kishon Vijay Abraham I <kishon@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org, 
	linux-phy@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Krzysztof Kozlowski <krzk@...nel.org>, 
	Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: phy: qcom,sc8280xp-qmp-pcie-phy:
 Document the X1E80100 QMP PCIe PHY Gen4 x4

On Fri, 30 Aug 2024 at 15:09, Johan Hovold <johan@...nel.org> wrote:
>
> On Fri, Aug 30, 2024 at 01:42:10PM +0300, Dmitry Baryshkov wrote:
> > On Fri, Aug 23, 2024 at 10:04:15AM GMT, Abel Vesa wrote:
> > > The sixth PCIe instance on X1E80100 can be used in either 4-lane mode or
> > > 2-lane mode. Document the 4-lane mode as a separate compatible.
> >
> > As the patches were merged, it's too late for this series, but as a
> > note: we should think of a way to describe the PHY configuration without
> > changing the compatibility strings. The hardware stays the same, it's
> > just the number of lanes being wired that changes.
>
> No, this is not about configuration and we need two separate compatibles
> as the two PHY instances are distinct and only one of them can be used
> in 4-lane mode.

Ack, makes sense.

> The mistake was to ever describe pcie6a as 2-lane in the x1e80100 dtsi
> (and possibly also in the ambiguous commit message above). Whether
> pcie6a is used in 4-lane or 2-lane mode is determined by a TCSR
> register.

Yes, I was confused by the commit message. I assumed that the
compatible string is used to switch PHY modes. Had the patchset come
with the DT patch, it would be easier to understand what was going on.

-- 
With best wishes
Dmitry