linux-kernel - RE: [PATCH v2 1/2] ARM: dts: imx6qp-sabresd: Enable PCIe support

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Date:   Mon, 14 Feb 2022 01:18:49 +0000
From:   Hongxing Zhu <hongxing.zhu@....com>
To:     Shawn Guo <shawnguo@...nel.org>
CC:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "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>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH v2 1/2] ARM: dts: imx6qp-sabresd: Enable PCIe support

> -----Original Message-----
> From: Shawn Guo <shawnguo@...nel.org>
> Sent: 2022年2月13日 12:32
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: l.stach@...gutronix.de; bhelgaas@...gle.com;
> lorenzo.pieralisi@....com; linux-pci@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> kernel@...gutronix.de; dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH v2 1/2] ARM: dts: imx6qp-sabresd: Enable PCIe support
> 
> On Fri, Feb 11, 2022 at 03:32:58PM +0800, Richard Zhu wrote:
> > In the i.MX6QP sabresd board(sch-28857) design, one external
> > oscillator is used as the PCIe reference clock source by the endpoint device.
> >
> > If RC uses this oscillator as reference clock too, PLL6(ENET PLL)
> > would has to be in bypass mode, and ENET clocks would be messed up.
> >
> > To keep things simple, let RC use the internal PLL as reference clock
> > and always enable the external oscillator for endpoint device on
> > i.MX6QP sabresd board.
> >
> > NOTE: This reference clock setup is used to pass the GEN2 TX
> > compliance tests, and isn't recommended as a setup in the end-user design.
> 
> I do not quite follow.  The commit log is all talking about external oscillator
> reference clock, while code is playing 'vgen3' regulator.
Hi Shawn:
The vgen3 is the power-supply used to power up the external OSC circuit on
 the board.
Set vgen2 always on to toggle the external OSC and provide the REF clock
 for EP device once the board is powered up.

Thanks.
Best Regards
Richard
> 
> Shawn
> 
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> >  arch/arm/boot/dts/imx6qp-sabresd.dts | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/boot/dts/imx6qp-sabresd.dts
> > b/arch/arm/boot/dts/imx6qp-sabresd.dts
> > index 480e73183f6b..083cf90bcab5 100644
> > --- a/arch/arm/boot/dts/imx6qp-sabresd.dts
> > +++ b/arch/arm/boot/dts/imx6qp-sabresd.dts
> > @@ -50,8 +50,14 @@ MX6QDL_PAD_SD3_DAT7__SD3_DATA7
> 	0x17059
> >  	};
> >  };
> >
> > +&vgen3_reg {
> > +	regulator-min-microvolt = <1800000>;
> > +	regulator-max-microvolt = <3300000>;
> > +	regulator-always-on;
> > +};
> > +
> >  &pcie {
> > -	status = "disabled";
> > +	status = "okay";
> >  };
> >
> >  &sata {
> > --
> > 2.25.1
> >