linux-kernel - Re: [PATCH v6 2/5] PCI: qcom: Add retry logic for link to be stable in L1ss

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Message-ID: <7310fc0c-5f87-87a6-4484-d60970ce3285@quicinc.com>
Date:   Mon, 12 Sep 2022 21:39:36 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     <linux-pci@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <mka@...omium.org>,
        <quic_vbadigan@...cinc.com>, <quic_hemantk@...cinc.com>,
        <quic_nitegupt@...cinc.com>, <quic_skananth@...cinc.com>,
        <quic_ramkri@...cinc.com>, <manivannan.sadhasivam@...aro.org>,
        <swboyd@...omium.org>, <dmitry.baryshkov@...aro.org>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v6 2/5] PCI: qcom: Add retry logic for link to be stable
 in L1ss


On 9/10/2022 1:20 AM, Bjorn Helgaas wrote:
> On Fri, Sep 09, 2022 at 02:14:41PM +0530, Krishna chaitanya chundru wrote:
>> Some specific devices are taking time to settle the link in L1ss.
>> So added a retry logic before returning from the suspend op.
> "L1ss" is not a state.  If you mean "L1.1" or "L1.2", say that.  Also
> in code comments below.
Yes L1ss means L1.2 and L1.2 We will update it next patch
> s/So added a/Add/
>
> What are these specific devices?  Is this a qcom controller defect?
> An endpoint defect that should be addressed via some kind of generic
> quirk?

This is depending up on the endpoint devices and it varies to device to 
device.

We are thinking this is not a defect if there is some traffic in the 
link the link will

not go to L1ss .

>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
>> ---
>>   drivers/pci/controller/dwc/pcie-qcom.c | 36 +++++++++++++++++++++++-----------
>>   1 file changed, 25 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
>> index 6e04d0d..15c2067 100644
>> --- a/drivers/pci/controller/dwc/pcie-qcom.c
>> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
>> @@ -1809,26 +1809,40 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>>   static int __maybe_unused qcom_pcie_pm_suspend(struct qcom_pcie *pcie)
>>   {
>>   	u32 val;
>> +	ktime_t timeout, start;
>>   	struct dw_pcie *pci = pcie->pci;
>>   	struct device *dev = pci->dev;
>>   
>>   	if (!pcie->cfg->supports_system_suspend)
>>   		return 0;
>>   
>> -	/* if the link is not active turn off clocks */
>> -	if (!dw_pcie_link_up(pci)) {
>> -		dev_info(dev, "Link is not active\n");
>> -		goto suspend;
>> -	}
>> +	start = ktime_get();
>> +	/* Wait max 200 ms */
>> +	timeout = ktime_add_ms(start, 200);
>>   
>> -	/* if the link is not in l1ss don't turn off clocks */
>> -	val = readl(pcie->parf + PCIE20_PARF_PM_STTS);
>> -	if (!(val & PCIE20_PARF_PM_STTS_LINKST_IN_L1SUB)) {
>> -		dev_warn(dev, "Link is not in L1ss\n");
>> -		return 0;
>> +	while (1) {
>> +
>> +		if (!dw_pcie_link_up(pci)) {
>> +			dev_warn(dev, "Link is not active\n");
>> +			break;
>> +		}
>> +
>> +		/* if the link is not in l1ss don't turn off clocks */
>> +		val = readl(pcie->parf + PCIE20_PARF_PM_STTS);
>> +		if ((val & PCIE20_PARF_PM_STTS_LINKST_IN_L1SUB)) {
>> +			dev_dbg(dev, "Link enters L1ss after %d  ms\n",
>> +					ktime_to_ms(ktime_get() - start));
>> +			break;
>> +		}
>> +
>> +		if (ktime_after(ktime_get(), timeout)) {
>> +			dev_warn(dev, "Link is not in L1ss\n");
>> +			return 0;
>> +		}
>> +
>> +		udelay(1000);
>>   	}
>>   
>> -suspend:
>>   	if (pcie->cfg->ops->suspend)
>>   		pcie->cfg->ops->suspend(pcie);
>>   
>> -- 
>> 2.7.4
>>