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

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Date:   Mon, 12 Sep 2022 23:03:46 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
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 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 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

> > 
> > > 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
> > >