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: <e9c5d29a-f1a7-46c8-a456-6c75c129876f@quicinc.com>
Date:   Tue, 13 Sep 2022 19:54:22 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
CC:     Bjorn Helgaas <helgaas@...nel.org>, <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>,
        <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 9/12/2022 11:03 PM, Manivannan Sadhasivam wrote:
> On Mon, Sep 12, 2022 at 09:39:36PM +0530, Krishna Chaitanya Chundru wrote:
>> 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.
>>
> Can we identify the source of the traffic? Is the NVMe driver not
> flushing it's queues correctly?

We found that it is not from nvme data, we are seeing some physical 
layer activity on the

protocol analyzer.

>
>> We are thinking this is not a defect if there is some traffic in the link
>> the link will
>>
>> not go to L1ss .
>>
> Is this hack still required even after switching to syscore ops?
>
> Thanks,
> Mani

Yes, mani it is still required. And just before this sycore ops there 
will be a pci transaction to

mask msix interrupts.

>>>> 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
>>>>