linux-kernel - Re: [PATCH v2] PCI: keystone: Fix race condition when initializing PHYs

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Message-ID: <cb19cfd1-22ed-7880-9fe-8b31488b6bb1@linux.intel.com>
Date:   Tue, 26 Sep 2023 19:38:16 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Siddharth Vadapalli <s-vadapalli@...com>
cc:     lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, vigneshr@...com,
        r-gunasekaran@...com, srk@...com
Subject: Re: [PATCH v2] PCI: keystone: Fix race condition when initializing
 PHYs

On Tue, 26 Sep 2023, Siddharth Vadapalli wrote:

> The PCI driver invokes the PHY APIs using the ks_pcie_enable_phy()
> function. The PHY in this case is the Serdes. It is possible that the
> PCI instance is configured for 2 lane operation across two different
> Serdes instances, using 1 lane of each Serdes. In such a configuration,
> if the reference clock for one Serdes is provided by the other Serdes,
> it results in a race condition. After the Serdes providing the reference
> clock is initialized by the PCI driver by invoking its PHY APIs, it is
> not guaranteed that this Serdes remains powered on long enough for the
> PHY APIs based initialization of the dependent Serdes. In such cases,
> the PLL of the dependent Serdes fails to lock due to the absence of the
> reference clock from the former Serdes which has been powered off by the
> PM Core.
> 
> Fix this by obtaining reference to the PHYs before invoking the PHY
> initialization APIs and releasing reference after the initialization is
> complete.
> 
> Fixes: 49229238ab47 ("PCI: keystone: Cleanup PHY handling")
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
> ---
> 
> NOTE: This patch is based on linux-next tagged next-20230925.
> 
> v1:
> https://lore.kernel.org/r/20230926054200.963803-1-s-vadapalli@ti.com/
> 
> Changes since v1:
> - Add code to release reference(s) to the phy(s) when
>   ks_pcie_enable_phy(ks_pcie) fails.
> 
> Regards,
> Siddharth.
> 
>  drivers/pci/controller/dwc/pci-keystone.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
> index 49aea6ce3e87..e4d43306a7e3 100644
> --- a/drivers/pci/controller/dwc/pci-keystone.c
> +++ b/drivers/pci/controller/dwc/pci-keystone.c
> @@ -1218,12 +1218,24 @@ static int __init ks_pcie_probe(struct platform_device *pdev)
>  		goto err_link;
>  	}
>  
> +	/* Obtain reference(s) to the phy(s) */
> +	for (i = 0; i < num_lanes; i++)
> +		phy_pm_runtime_get_sync(ks_pcie->phy[i]);
> +
>  	ret = ks_pcie_enable_phy(ks_pcie);

You could do the put loop here before checking ret to avoid duplicating 
the put loop.

>  	if (ret) {
>  		dev_err(dev, "failed to enable phy\n");
> +		/* Release reference(s) to the phy(s) */
> +		for (i = 0; i < num_lanes; i++)
> +			phy_pm_runtime_put_sync(ks_pcie->phy[i]);
> +
>  		goto err_link;
>  	}
>  
> +	/* Release reference(s) to the phy(s) */
> +	for (i = 0; i < num_lanes; i++)
> +		phy_pm_runtime_put_sync(ks_pcie->phy[i]);
> +
>  	platform_set_drvdata(pdev, ks_pcie);
>  	pm_runtime_enable(dev);
>  	ret = pm_runtime_get_sync(dev);
> 

-- 
 i.