linux-kernel - Re: [PATCH v3 2/2] PCI: layerscape: Add the workaround for lost link capabilities during reset.

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Message-ID: <ZLhiYlGBHX6ra5zf@lizhi-Precision-Tower-5810>
Date:   Wed, 19 Jul 2023 18:23:30 -0400
From:   Frank Li <Frank.li@....com>
To:     markus.elfring@....de, lpieralisi@...nel.org
Cc:     Zhiqiang.Hou@....com, bhelgaas@...gle.com, imx@...ts.linux.dev,
        kernel-janitors@...r.kernel.org, kw@...ux.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        mani@...nel.org, minghuan.Lian@....com, mingkai.hu@....com,
        robh@...nel.org, roy.zang@....com, xiaowei.bao@....com
Subject: Re: [PATCH v3 2/2] PCI: layerscape: Add the workaround for lost link
 capabilities during reset.

On Wed, Jul 19, 2023 at 11:57:07AM -0400, Frank Li wrote:
> From: Xiaowei Bao <xiaowei.bao@....com>
> 
> A workaround for the issue where the PCI Express Endpoint (EP) controller
> loses the values of the Maximum Link Width and Supported Link Speed from
> the Link Capabilities Register, which initially configured by the Reset
> Configuration Word (RCW) during a link-down or hot reset event.
> 
> Fixes: a805770d8a22 ("PCI: layerscape: Add EP mode support")
> Acked-by: Manivannan Sadhasivam <mani@...nel.org>
> Signed-off-by: Xiaowei Bao <xiaowei.bao@....com>
> Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@....com>
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
> change from v2 to v3
>  - fix subject typo capabilities
> change from v1 to v2:
>  - add comments at restore register
>  - add fixes tag
>  - dw_pcie_writew_dbi to dw_pcie_writel_dbi
> 
>  .../pci/controller/dwc/pci-layerscape-ep.c    | 21 ++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-layerscape-ep.c b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> index e0969ff2ddf7..39dbd911c3f8 100644
> --- a/drivers/pci/controller/dwc/pci-layerscape-ep.c
> +++ b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> @@ -45,6 +45,7 @@ struct ls_pcie_ep {
>  	struct pci_epc_features		*ls_epc;
>  	const struct ls_pcie_ep_drvdata *drvdata;
>  	int				irq;
> +	u32				lnkcap;
>  	bool				big_endian;
>  };
>  
> @@ -73,6 +74,7 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
>  	struct ls_pcie_ep *pcie = dev_id;
>  	struct dw_pcie *pci = pcie->pci;
>  	u32 val, cfg;
> +	u8 offset;
>  
>  	val = ls_lut_readl(pcie, PEX_PF0_PME_MES_DR);
>  	ls_lut_writel(pcie, PEX_PF0_PME_MES_DR, val);
> @@ -81,12 +83,25 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
>  		return IRQ_NONE;
>  
>  	if (val & PEX_PF0_PME_MES_DR_LUD) {
> +
> +		offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +
> +		/*
> +		 * The values of the Maximum Link Width and Supported Link
> +		 * Speed from the Link Capabilities Register will be lost
> +		 * during link down or hot reset. Restore initial value
> +		 * that configured by the Reset Configuration Word (RCW).
> +		 */
> +		dw_pcie_dbi_ro_wr_en(pci);
> +		dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, pcie->lnkcap);
> +		dw_pcie_dbi_ro_wr_dis(pci);
> +
>  		cfg = ls_lut_readl(pcie, PEX_PF0_CONFIG);
>  		cfg |= PEX_PF0_CFG_READY;
>  		ls_lut_writel(pcie, PEX_PF0_CONFIG, cfg);
>  		dw_pcie_ep_linkup(&pci->ep);
>  
> -		dev_dbg(pci->dev, "Link up\n");
> +		dev_err(pci->dev, "Link up\n");

Sorry, Just found that. mistake merge a debug code.
It should be dev_dbg here, will send update patch soon

Frank

>  	} else if (val & PEX_PF0_PME_MES_DR_LDD) {
>  		dev_dbg(pci->dev, "Link down\n");
>  		pci_epc_linkdown(pci->ep.epc);
> @@ -216,6 +231,7 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
>  	struct ls_pcie_ep *pcie;
>  	struct pci_epc_features *ls_epc;
>  	struct resource *dbi_base;
> +	u8 offset;
>  	int ret;
>  
>  	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
> @@ -252,6 +268,9 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, pcie);
>  
> +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	pcie->lnkcap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
> +
>  	ret = dw_pcie_ep_init(&pci->ep);
>  	if (ret)
>  		return ret;
> -- 
> 2.34.1
>