Re: [PATCH v8 3/7] PCI: qcom: Add ICC bandwidth vote for CPU to PCIe path

[Manivannan Sadhasivam <mani@kernel.org>]

On Sat, Mar 02, 2024 at 09:29:57AM +0530, Krishna chaitanya chundru wrote:
> To access PCIe registers, PCIe BAR space, config space the CPU-PCIe
> ICC (interconnect consumers) path should be voted otherwise it may
> lead to NoC (Network on chip) timeout. We are surviving because of
> other driver vote for this path.
> 
> As there is less access on this path compared to PCIe to mem path
> add minimum vote i.e 1KBps bandwidth always.

Please add the info that 1KBps is what shared by the HW team.

> 
> When suspending, disable this path after register space access
> is done.
> 
> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 38 ++++++++++++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 10f2d0bb86be..a0266bfe71f1 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -240,6 +240,7 @@ struct qcom_pcie {
>  	struct phy *phy;
>  	struct gpio_desc *reset;
>  	struct icc_path *icc_mem;
> +	struct icc_path *icc_cpu;
>  	const struct qcom_pcie_cfg *cfg;
>  	struct dentry *debugfs;
>  	bool suspended;
> @@ -1372,6 +1373,9 @@ static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
>  	if (IS_ERR(pcie->icc_mem))
>  		return PTR_ERR(pcie->icc_mem);
>  
> +	pcie->icc_cpu = devm_of_icc_get(pci->dev, "cpu-pcie");
> +	if (IS_ERR(pcie->icc_cpu))
> +		return PTR_ERR(pcie->icc_cpu);
>  	/*
>  	 * Some Qualcomm platforms require interconnect bandwidth constraints
>  	 * to be set before enabling interconnect clocks.
> @@ -1381,7 +1385,19 @@ static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
>  	 */
>  	ret = icc_set_bw(pcie->icc_mem, 0, QCOM_PCIE_LINK_SPEED_TO_BW(1));
>  	if (ret) {
> -		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
> +		dev_err(pci->dev, "failed to set interconnect bandwidth for pcie-mem: %d\n",

"PCIe-MEM"

> +			ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * The config space, BAR space and registers goes through cpu-pcie path
> +	 * Set peak bandwidth to 1KBps as recommended by HW team for this path
> +	 * all the time.

How about,

	"Since the CPU-PCIe path is only used for activities like register
	access, Config/BAR space access, HW team has recommended to use a
	minimal bandwidth of 1KBps just to keep the link active."

> +	 */
> +	ret = icc_set_bw(pcie->icc_cpu, 0, kBps_to_icc(1));
> +	if (ret) {
> +		dev_err(pci->dev, "failed to set interconnect bandwidth for cpu-pcie: %d\n",
>  			ret);
>  		return ret;
>  	}
> @@ -1573,7 +1589,7 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
>  	 */
>  	ret = icc_set_bw(pcie->icc_mem, 0, kBps_to_icc(1));
>  	if (ret) {
> -		dev_err(dev, "Failed to set interconnect bandwidth: %d\n", ret);
> +		dev_err(dev, "Failed to set interconnect bandwidth for pcie-mem: %d\n", ret);

"PCIe-MEM"

>  		return ret;
>  	}
>  
> @@ -1597,6 +1613,18 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
>  		pcie->suspended = true;
>  	}
>  
> +	/* Remove CPU path vote after all the register access is done */

"Remove the vote for CPU-PCIe path now, since at this point onwards, no register
access will be done."

> +	ret = icc_disable(pcie->icc_cpu);
> +	if (ret) {
> +		dev_err(dev, "failed to disable icc path of cpu-pcie: %d\n", ret);

"CPU-PCIe"

> +		if (pcie->suspended) {
> +			qcom_pcie_host_init(&pcie->pci->pp);

Interesting. So if icc_disable() fails, can the IP continue to function?

> +			pcie->suspended = false;
> +		}
> +		qcom_pcie_icc_update(pcie);
> +		return ret;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1605,6 +1633,12 @@ static int qcom_pcie_resume_noirq(struct device *dev)
>  	struct qcom_pcie *pcie = dev_get_drvdata(dev);
>  	int ret;
>  
> +	ret = icc_enable(pcie->icc_cpu);
> +	if (ret) {
> +		dev_err(dev, "failed to enable icc path of cpu-pcie: %d\n", ret);

"CPU-PCIe"

- Mani

-- 
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