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: <51be0ae5-8f48-fc6e-0246-810018326594@quicinc.com>
Date:   Wed, 14 Sep 2022 07:15:35 +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 9/13/2022 10:09 PM, Manivannan Sadhasivam wrote:
> On Tue, Sep 13, 2022 at 07:54:22PM +0530, Krishna Chaitanya Chundru wrote:
>> 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.
>>
> Okay
>
>>>> 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.
>>
> Hmm. I'm getting slightly confused here. What really happens when you do
> the resource teardown during suspend and the link has not entered L1SS?
>
> Since PHY is powered by MX domain, I'm wondering why we should wait for
> the link to be in L1SS?
>
> Thanks,
> Mani

Mani, we need to turn off the link only after link entered in to L1ss. 
If we do before that

some transactions will be disturbed and we see a link down.

Mx power rail will control digital logic of the PHY and tries to retain 
the link state only,

The analog logic is controlled by the CX rail only, so when the link is 
in L1ss only we turn off

clks and phy.

>>>>>> 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
>>>>>>