linux-kernel - Re: [PATCH v7 2/2] PCI: cadence: Retrain Link to work around Gen2 training defect.

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Message-ID: <20210208183147.GA12258@e121166-lin.cambridge.arm.com>
Date:   Mon, 8 Feb 2021 18:31:47 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Nadeem Athani <nadeem@...ence.com>
Cc:     tjoseph@...ence.com, robh@...nel.org, bhelgaas@...gle.com,
        kishon@...com, linux-omap@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, mparab@...ence.com,
        sjakhade@...ence.com, pthombar@...ence.com
Subject: Re: [PATCH v7 2/2] PCI: cadence: Retrain Link to work around Gen2
 training defect.

On Wed, Dec 30, 2020 at 01:05:15PM +0100, Nadeem Athani wrote:
> Cadence controller will not initiate autonomous speed change if strapped
> as Gen2. The Retrain Link bit is set as quirk to enable this speed change.
> 
> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
> ---
>  drivers/pci/controller/cadence/pci-j721e.c         |  3 ++
>  drivers/pci/controller/cadence/pcie-cadence-host.c | 37 +++++++++++++++++++++-
>  drivers/pci/controller/cadence/pcie-cadence.h      | 11 ++++++-
>  3 files changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index dac1ac8a7615..849f1e416ea5 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -64,6 +64,7 @@ enum j721e_pcie_mode {
>  
>  struct j721e_pcie_data {
>  	enum j721e_pcie_mode	mode;
> +	bool quirk_retrain_flag;
>  };
>  
>  static inline u32 j721e_pcie_user_readl(struct j721e_pcie *pcie, u32 offset)
> @@ -280,6 +281,7 @@ static struct pci_ops cdns_ti_pcie_host_ops = {
>  
>  static const struct j721e_pcie_data j721e_pcie_rc_data = {
>  	.mode = PCI_MODE_RC,
> +	.quirk_retrain_flag = true,
>  };
>  
>  static const struct j721e_pcie_data j721e_pcie_ep_data = {
> @@ -388,6 +390,7 @@ static int j721e_pcie_probe(struct platform_device *pdev)
>  
>  		bridge->ops = &cdns_ti_pcie_host_ops;
>  		rc = pci_host_bridge_priv(bridge);
> +		rc->quirk_retrain_flag = data->quirk_retrain_flag;
>  
>  		cdns_pcie = &rc->pcie;
>  		cdns_pcie->dev = dev;
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> index 9f7aa718c8d4..f3496588862d 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> @@ -94,6 +94,35 @@ static int cdns_pcie_host_wait_for_link(struct cdns_pcie *pcie)
>  	return -ETIMEDOUT;
>  }
>  
> +static int cdns_pcie_retrain(struct cdns_pcie *pcie)
> +{
> +	u32 lnk_cap_sls, pcie_cap_off = CDNS_PCIE_RP_CAP_OFFSET;
> +	u16 lnk_stat, lnk_ctl;
> +	int ret = 0;
> +
> +	/*
> +	 * Set retrain bit if current speed is 2.5 GB/s,
> +	 * but the PCIe root port support is > 2.5 GB/s.
> +	 */
> +
> +	lnk_cap_sls = cdns_pcie_readl(pcie, (CDNS_PCIE_RP_BASE + pcie_cap_off +
> +					     PCI_EXP_LNKCAP));
> +	if ((lnk_cap_sls & PCI_EXP_LNKCAP_SLS) <= PCI_EXP_LNKCAP_SLS_2_5GB)
> +		return ret;
> +
> +	lnk_stat = cdns_pcie_rp_readw(pcie, pcie_cap_off + PCI_EXP_LNKSTA);
> +	if ((lnk_stat & PCI_EXP_LNKSTA_CLS) == PCI_EXP_LNKSTA_CLS_2_5GB) {
> +		lnk_ctl = cdns_pcie_rp_readw(pcie,
> +					     pcie_cap_off + PCI_EXP_LNKCTL);
> +		lnk_ctl |= PCI_EXP_LNKCTL_RL;
> +		cdns_pcie_rp_writew(pcie, pcie_cap_off + PCI_EXP_LNKCTL,
> +				    lnk_ctl);
> +
> +		ret = cdns_pcie_host_wait_for_link(pcie);
> +	}
> +	return ret;
> +}
> +
>  static int cdns_pcie_host_init_root_port(struct cdns_pcie_rc *rc)
>  {
>  	struct cdns_pcie *pcie = &rc->pcie;
> @@ -457,8 +486,14 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>  	}
>  
>  	ret = cdns_pcie_host_wait_for_link(pcie);
> -	if (ret)
> +	if (ret) {
>  		dev_dbg(dev, "PCIe link never came up\n");
> +	} else {
> +		if (rc->quirk_retrain_flag) {
> +			if (cdns_pcie_retrain(pcie))
> +				dev_dbg(dev, "PCIe link never came up\n");

I'd move this whole if/else in a function cdns_pcie_host_start_link(),
IMO that's cleaner.

static int cdns_pcie_host_start_link(struct cdns_pcie_rc *rc)
{
	struct cdns_pcie *pcie = &rc->pcie;
	int ret;

	ret = cdns_pcie_host_wait_for_link(pcie);
	/*
	 * PLS ADD A COMMENT HERE
	 */
	if (!ret && rc->quirk_retrain_flag)
		ret = cdns_pcie_retrain(pcie);

	return ret;
}