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

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Date:   Mon, 22 Mar 2021 13:14:39 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Richard Zhu <hongxing.zhu@....com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "stefan@...er.ch" <stefan@...er.ch>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the imx8mq
 pcie phy voltage

Hi Richard,

Am Montag, dem 22.03.2021 um 09:06 +0000 schrieb Richard Zhu:
> > -----Original Message-----
> > From: Lucas Stach <l.stach@...gutronix.de>
> > Sent: Friday, March 19, 2021 5:49 PM
> > 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; dl-linux-imx <linux-imx@....com>;
> > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> > kernel@...gutronix.de
> > Subject: [EXT] 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.
> > 
> [Richard Zhu] Hi Lucas:
> Thanks for your comments. Since the vgen5_reg is used to power up
> PCIe PHY on i.MX8MQ EVK board,
>  and it's set to be "regulator-always-on;".
> Did only the regulator_get_voltage or combined with
> regulator_enable/regulator_disable can be used in the driver?

The regulator API doesn't care, you can call enable/disable in the
driver as normal. If the regulator is marked as always-on it will just
stay enabled even if the use-count drops to 0.

The other question however is if it's even allowed by the SoC design to
disable this supply outside of deep power down. A quick look into the
reference manual and datasheet didn't yield any information about this.

Regards,
Lucas