linux-kernel - RE: [PATCH] PCI: imx6: Override the CLKREQ low in the initialization

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Date:   Thu, 24 Feb 2022 02:04:25 +0000
From:   Hongxing Zhu <hongxing.zhu@....com>
To:     Bjorn Helgaas <helgaas@...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] PCI: imx6: Override the CLKREQ low in the initialization

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@...nel.org>
> Sent: 2022年2月24日 2:32
> 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] PCI: imx6: Override the CLKREQ low in the initialization
> 
> In subject, maybe:
> 
>   PCI: imx6: Assert i.MX8MM CLKREQ# even if no device present
> 
> On Wed, Feb 23, 2022 at 04:38:33PM +0800, Richard Zhu wrote:
> > The CLKREQ# signal is an open drain, active low signal that is driven
> > low by the remote Endpoint device. But it might not be driven low if
> > no Endpoint device is connected.
> >
> > On i.MX8MM PCIe, phy_init() would be failed and system boot hang if
> > the reference clock is not toggled.
> 
> s/would be failed/may fail/
> s/boot hang/boot may hang/
> s/if the reference clock is not toggled/if no Endpoint is connected to assert
> CLKREQ#/
> 
> > Follow with i.MX8MQ PCIe, to make sure the reference clock on,
> > override the CLKREQ# low during initialization to fix this issue.
> 
>   Handle this as on i.MX8MQ, where we explicitly assert CLKREQ# so the
>   PHY can be initialized.
> 
> (I don't really understand the hardware here, so disregard if this doesn't say
> what it needs to.)
Hi Bjorn:
Thanks a lot.
Your description is much better than mine.
Would be changed later.

Best Regards
Richard Zhu

> 
> > Fixes: 178e244cb6e2 ("PCI: imx: Add the imx8mm pcie support")
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index d7f0db01f3c3..a334341a1789 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -447,10 +447,6 @@ static int imx6_pcie_enable_ref_clk(struct
> imx6_pcie *imx6_pcie)
> >  	case IMX7D:
> >  		break;
> >  	case IMX8MM:
> > -		ret = clk_prepare_enable(imx6_pcie->pcie_aux);
> > -		if (ret)
> > -			dev_err(dev, "unable to enable pcie_aux clock\n");
> > -		break;
> >  	case IMX8MQ:
> >  		ret = clk_prepare_enable(imx6_pcie->pcie_aux);
> >  		if (ret) {
> > --
> > 2.25.1
> >