linux-kernel - Re: [PATCH 09/15] dt-bindings: phy: qcom,qmp-pcie: mark current bindings as legacy

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Date:   Tue, 18 Oct 2022 12:52:03 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Vinod Koul <vkoul@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/15] dt-bindings: phy: qcom,qmp-pcie: mark current
 bindings as legacy

Hi,

On Mon, 17 Oct 2022 at 17:54, Johan Hovold <johan+linaro@...nel.org> wrote:
>
> The current QMP PCIe PHY bindings are based on the original MSM8996
> binding which provided multiple PHYs per IP block and these in turn were
> described by child nodes.
>
> Later QMP PCIe PHY blocks only provide a single PHY and the remnant
> child node does not really reflect the hardware.
>
> The original MSM8996 binding also ended up describing the individual
> register blocks as belonging to either the wrapper node or the PHY child
> nodes.
>
> This is an unnecessary level of detail which has lead to problems when
> later IP blocks using different register layouts have been forced to fit
> the original mould rather than updating the binding. The bindings are
> arguable also incomplete as they only the describe register blocks used
> by the current Linux drivers (e.g. does not include the per lane PCS
> registers).

I'd like to point out that it's not only a problem peculiar to the
PCIe PHYs. Other QMP PHY families also follow the same approach of
separating the serdes into the common part and rx/tx/PCS/whatever into
the PHY subnodes.
For the USB+DP combo PHYs we have to have subnodes, however it would
also be logical to move serdes register to the subnode devices,
leaving only DP_COM in the base node.

That said, I think we should rethink and agree on QMP PHY bindings,
before renaming the bindings. And yes, I think we should also upgrade
older DTs, keeping drivers backwards compatible (for some time?).

> In preparation for adding new bindings for SC8280XP which further
> bindings can be based on, mark the current bindings as "legacy".
>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>  .../{qcom,qmp-pcie-phy.yaml => qcom,qmp-pcie-phy-legacy.yaml} | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>  rename Documentation/devicetree/bindings/phy/{qcom,qmp-pcie-phy.yaml => qcom,qmp-pcie-phy-legacy.yaml} (98%)

-- 
With best wishes
Dmitry