linux-kernel - Re: [PATCH v2] PCI: dwc: Wait for link up only if link is started

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Date:   Fri, 7 Apr 2023 10:40:01 -0700
From:   William McVicker <willmcvicker@...gle.com>
To:     Ajay Agarwal <ajayagarwal@...gle.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sajid Dalvi <sdalvi@...gle.com>,
        Han Jingoo <jingoohan1@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>, kernel-team@...roid.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v2] PCI: dwc: Wait for link up only if link is started

On 04/06/2023, 'Ajay Agarwal' via kernel-team wrote:
> Here is my attempt at a patch which can satisfy all the requirements
> (Ideally, I did not want to use `pci->ops` in the host driver but I
> could not figure out any other way):
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 9952057c8819..39c7219ec7c9 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -485,15 +485,18 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	if (ret)
>  		goto err_remove_edma;
>  
> -	if (!dw_pcie_link_up(pci)) {
> -		ret = dw_pcie_start_link(pci);
> +	ret = dw_pcie_start_link(pci);
> +	if (ret)
> +		goto err_remove_edma;
> +
> +	if (dw_pcie_link_up(pci)) {
> +		dw_pcie_print_link_status(pci);
> +	} else if (pci->ops && pci->ops->start_link) {
> +		ret = dw_pcie_wait_for_link(pci);
>  		if (ret)
> -			goto err_remove_edma;
> +			goto err_stop_link;
>  	}
>  
> -	/* Ignore errors, the link may come up later */
> -	dw_pcie_wait_for_link(pci);
> -
>  	bridge->sysdata = pp;
>  
>  	ret = pci_host_probe(bridge);
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 53a16b8b6ac2..03748a8dffd3 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -644,9 +644,20 @@ void dw_pcie_disable_atu(struct dw_pcie *pci, u32 dir, int index)
>  	dw_pcie_writel_atu(pci, dir, index, PCIE_ATU_REGION_CTRL2, 0);
>  }
>  
> -int dw_pcie_wait_for_link(struct dw_pcie *pci)
> +void dw_pcie_print_link_status(struct dw_pcie *pci)
>  {
>  	u32 offset, val;
> +
> +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
> +
> +	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
> +		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
> +		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
> +}
> +
> +int dw_pcie_wait_for_link(struct dw_pcie *pci)
> +{
>  	int retries;
>  
>  	/* Check if the link is up or not */
> @@ -662,12 +673,7 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
>  		return -ETIMEDOUT;
>  	}
>  
> -	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> -	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
> -
> -	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
> -		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
> -		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
> +	dw_pcie_print_link_status(pci);
>  
>  	return 0;
>  }
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 79713ce075cc..615660640801 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -429,6 +429,7 @@ void dw_pcie_setup(struct dw_pcie *pci);
>  void dw_pcie_iatu_detect(struct dw_pcie *pci);
>  int dw_pcie_edma_detect(struct dw_pcie *pci);
>  void dw_pcie_edma_remove(struct dw_pcie *pci);
> +void dw_pcie_print_link_status(struct dw_pcie *pci);
>  
>  static inline void dw_pcie_writel_dbi(struct dw_pcie *pci, u32 reg, u32 val)
>  {
> 
> -- 
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> 

Thanks Ajay for the follow-up patch! I've tested it out on a Pixel 6 and
it's working as intended for me. Probing the PCIe RC device now only
take 0.02s vs ~1.02s. If others don't object, please send it as a v3
patch.

Thanks,
Will