linux-kernel - Re: [RESEND PATCH] PCI: cadence: Fix Gen2 Link Retraining process

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Message-ID: <cf8c7d73-1e51-7dcd-bb32-34272a63066f@ti.com>
Date:   Tue, 10 Jan 2023 16:03:39 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     <tjoseph@...ence.com>, <lpieralisi@...nel.org>, <robh@...nel.org>,
        <kw@...ux.com>, <bhelgaas@...gle.com>, <nadeem@...ence.com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <vigneshr@...com>,
        <srk@...com>, <nm@...com>, <s-vadapalli@...com>
Subject: Re: [RESEND PATCH] PCI: cadence: Fix Gen2 Link Retraining process

Hello All,

Can this patch please be merged in case of no feedback or issues?

Regards,
Siddharth.

On 02/01/23 13:26, Siddharth Vadapalli wrote:
> The Link Retraining process is initiated to account for the Gen2 defect in
> the Cadence PCIe controller in J721E SoC. The errata corresponding to this
> is i2085, documented at:
> https://www.ti.com/lit/er/sprz455c/sprz455c.pdf
> 
> The existing workaround implemented for the errata waits for the Data Link
> initialization to complete and assumes that the link retraining process
> at the Physical Layer has completed. However, it is possible that the
> Physical Layer training might be ongoing as indicated by the
> PCI_EXP_LNKSTA_LT bit in the PCI_EXP_LNKSTA register.
> 
> Fix the existing workaround, to ensure that the Physical Layer training
> has also completed, in addition to the Data Link initialization.
> 
> Fixes: 4740b969aaf5 ("PCI: cadence: Retrain Link to work around Gen2 training defect")
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
> ---
>  .../controller/cadence/pcie-cadence-host.c    | 27 +++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> index 940c7dd701d6..5b14f7ee3c79 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> @@ -12,6 +12,8 @@
>  
>  #include "pcie-cadence.h"
>  
> +#define LINK_RETRAIN_TIMEOUT HZ
> +
>  static u64 bar_max_size[] = {
>  	[RP_BAR0] = _ULL(128 * SZ_2G),
>  	[RP_BAR1] = SZ_2G,
> @@ -77,6 +79,27 @@ static struct pci_ops cdns_pcie_host_ops = {
>  	.write		= pci_generic_config_write,
>  };
>  
> +static int cdns_pcie_host_training_complete(struct cdns_pcie *pcie)
> +{
> +	u32 pcie_cap_off = CDNS_PCIE_RP_CAP_OFFSET;
> +	unsigned long end_jiffies;
> +	u16 lnk_stat;
> +
> +	/* Wait for link training to complete. Exit after timeout. */
> +	end_jiffies = jiffies + LINK_RETRAIN_TIMEOUT;
> +	do {
> +		lnk_stat = cdns_pcie_rp_readw(pcie, pcie_cap_off + PCI_EXP_LNKSTA);
> +		if (!(lnk_stat & PCI_EXP_LNKSTA_LT))
> +			break;
> +		usleep_range(0, 1000);
> +	} while (time_before(jiffies, end_jiffies));
> +
> +	if (!(lnk_stat & PCI_EXP_LNKSTA_LT))
> +		return 0;
> +
> +	return -ETIMEDOUT;
> +}
> +
>  static int cdns_pcie_host_wait_for_link(struct cdns_pcie *pcie)
>  {
>  	struct device *dev = pcie->dev;
> @@ -118,6 +141,10 @@ static int cdns_pcie_retrain(struct cdns_pcie *pcie)
>  		cdns_pcie_rp_writew(pcie, pcie_cap_off + PCI_EXP_LNKCTL,
>  				    lnk_ctl);
>  
> +		ret = cdns_pcie_host_training_complete(pcie);
> +		if (ret)
> +			return ret;
> +
>  		ret = cdns_pcie_host_wait_for_link(pcie);
>  	}
>  	return ret;