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

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Message-ID: <20220223183157.GA142509@bhelgaas>
Date:   Wed, 23 Feb 2022 12:31:57 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Richard 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, 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.)

> 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
>