linux-kernel - Re: [PATCH v3 1/1] PCI: qcom: Add support for system suspend and resume

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Message-ID: <ZCQLWzqKPrusMro+@hovoldconsulting.com>
Date:   Wed, 29 Mar 2023 11:56:43 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_krichai@...cinc.com, johan+linaro@...nel.org, steev@...i.org,
        mka@...omium.org, Dhruva Gole <d-gole@...com>
Subject: Re: [PATCH v3 1/1] PCI: qcom: Add support for system suspend and
 resume

On Mon, Mar 27, 2023 at 07:08:24PM +0530, Manivannan Sadhasivam wrote:
> During the system suspend, vote for minimal interconnect bandwidth and
> also turn OFF the resources like clock and PHY if there are no active
> devices connected to the controller. For the controllers with active
> devices, the resources are kept ON as removing the resources will
> trigger access violation during the late end of suspend cycle as kernel
> tries to access the config space of PCIe devices to mask the MSIs.
> 
> Also, it is not desirable to put the link into L2/L3 state as that
> implies VDD supply will be removed and the devices may go into powerdown
> state. This will affect the lifetime of storage devices like NVMe.
> 
> And finally, during resume, turn ON the resources if the controller was
> truly suspended (resources OFF) and update the interconnect bandwidth
> based on PCIe Gen speed.
> 
> Suggested-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> Acked-by: Dhruva Gole <d-gole@...com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 62 ++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index a232b04af048..f33df536d9be 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -227,6 +227,7 @@ struct qcom_pcie {
>  	struct gpio_desc *reset;
>  	struct icc_path *icc_mem;
>  	const struct qcom_pcie_cfg *cfg;
> +	bool suspended;
>  };
>  
>  #define to_qcom_pcie(x)		dev_get_drvdata((x)->dev)
> @@ -1820,6 +1821,62 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>  	return ret;
>  }
>  
> +static int qcom_pcie_suspend_noirq(struct device *dev)
> +{
> +	struct qcom_pcie *pcie = dev_get_drvdata(dev);
> +	int ret;
> +
> +	/*
> +	 * Set minimum bandwidth required to keep data path functional during
> +	 * suspend.
> +	 */
> +	ret = icc_set_bw(pcie->icc_mem, 0, MBps_to_icc(250));

This isn't really the minimum bandwidth you're setting here.

I think you said off list that you didn't see real impact reducing the
bandwidth, but have you tried requesting the real minimum which would be
kBps_to_icc(1)?

Doing so works fine here with both the CRD and X13s and may result in
some further power savings.

> +	if (ret) {
> +		dev_err(dev, "Failed to set interconnect bandwidth: %d\n", ret);
> +		return ret;
> +	}

Johan