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

[Siddharth Vadapalli <s-vadapalli@ti.com>]

On 26/09/23 22:08, Ilpo Järvinen wrote:
> 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@ti.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.

Right! Thank you for reviewing the patch and sharing this suggestion. I will
implement this and post the v3 patch.

> 
>>  	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);
>>
> 

-- 
Regards,
Siddharth.