linux-kernel - Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the imx8mq pcie phy voltage

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Date:   Fri, 19 Mar 2021 10:49:29 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Richard Zhu <hongxing.zhu@....com>, andrew.smirnov@...il.com,
        shawnguo@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        stefan@...er.ch, lorenzo.pieralisi@....com
Cc:     linux-pci@...r.kernel.org, linux-imx@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the imx8mq pcie
 phy voltage

Am Freitag, dem 19.03.2021 um 16:24 +0800 schrieb Richard Zhu:
> Both 1.8v and 3.3v power supplies can be feeded to i.MX8MQ PCIe PHY.
> In default, the PCIE_VPH voltage is suggested to be 1.8v refer to data
> sheet. When PCIE_VPH is supplied by 3.3v in the HW schematic design,
> the VREG_BYPASS bits of GPR registers should be cleared from default
> value 1b'1 to 1b'0.
> 
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
>  Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> index de4b2baf91e8..23efbad9e804 100644
> --- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> +++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
> @@ -59,6 +59,10 @@ Additional required properties for imx7d-pcie and imx8mq-pcie:
>  Additional required properties for imx8mq-pcie:
>  - clock-names: Must include the following additional entries:
>  	- "pcie_aux"
> +- pcie-vph-3v3: If present then PCIE_VPH is feeded by 3.3v in the HW
> +  schematic design. The PCIE_VPH is suggested to be 1.8v refer to the
> +  data sheet. If the PCIE_VPH is supplied by 3.3V, the VREG_BYPASS
> +  should be cleared to zero accordingly.

Uhm, no. Please don't add boolean DT properties for random parts of the
board design.

If we need to know the voltage of PCIE_VPH, we should really add the
VPH regulator as a supply to the PCIe controller node, then work out
the voltage the usual way by using the Linux regulator API.

Regards,
Lucas