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

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Date:   Fri, 9 Sep 2022 14:50:00 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>
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 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.

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?

> 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
>