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

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Message-ID: <VI1PR04MB585305B11C67D1F24A5D050C8C649@VI1PR04MB5853.eurprd04.prod.outlook.com>
Date:   Tue, 23 Mar 2021 06:54:53 +0000
From:   Richard Zhu <hongxing.zhu@....com>
To:     Lucas Stach <l.stach@...gutronix.de>,
        "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: Re: [PATCH 1/3] dt-bindings: imx6q-pcie: specify the imx8mq
 pcie phy voltage

> -----Original Message-----
> From: Lucas Stach <l.stach@...gutronix.de>
> Sent: Monday, March 22, 2021 8:15 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: 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: 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.
[Richard Zhu] Hi Lucas: Yes it is. The PCIe PHY power down manipulations are not
 described in the RM document.
How about to get voltage here only currently, and the regulator enable/disable operations
would be added further if these enable/disable operations are possible and required later?

Best Regards
Richard
> 
> Regards,
> Lucas