linux-kernel - Re: [PATCH v3] PCI: keystone: Fix race condition when initializing PHYs

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Date:   Wed, 15 Nov 2023 14:08:16 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     <bhelgaas@...gle.com>
CC:     <lpieralisi@...nel.org>, <robh@...nel.org>, <kw@...ux.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <ilpo.jarvinen@...ux.intel.com>, <vigneshr@...com>,
        Ravi Gunasekaran <r-gunasekaran@...com>, <srk@...com>,
        <s-vadapalli@...com>
Subject: Re: [PATCH v3] PCI: keystone: Fix race condition when initializing
 PHYs

Hello Bjorn,

Could you please merge this patch?

On 28/09/23 13:21, Ravi Gunasekaran wrote:
> 
> 
> On 9/27/23 9:48 AM, 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.
> 
> Sounds reasonable.
> 
> Acked-by: Ravi Gunasekaran <r-gunasekaran@...com>
> 
> Ravi
>>
>> 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-20230927.
>>
>> v2:
>> https://lore.kernel.org/r/20230926063638.1005124-1-s-vadapalli@ti.com/
>>
>> Changes since v2:
>> - Implement suggestion by Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>>   moving the phy_pm_runtime_put_sync() For-Loop section before the
>>   return value of ks_pcie_enable_phy(ks_pcie) is checked, thereby
>>   preventing duplication of the For-Loop.
>> - Rebase patch on next-20230927.
>>
>> 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 | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
>> index 49aea6ce3e87..0ec6720cc2df 100644
>> --- a/drivers/pci/controller/dwc/pci-keystone.c
>> +++ b/drivers/pci/controller/dwc/pci-keystone.c
>> @@ -1218,7 +1218,16 @@ 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);
>> +
>> +	/* Release reference(s) to the phy(s) */
>> +	for (i = 0; i < num_lanes; i++)
>> +		phy_pm_runtime_put_sync(ks_pcie->phy[i]);
>> +
>>  	if (ret) {
>>  		dev_err(dev, "failed to enable phy\n");
>>  		goto err_link;
> 

-- 
Regards,
Siddharth.