linux-kernel - Re: [PATCH v12 2/6] PCI: qcom: Add ICC bandwidth vote for CPU to PCIe path

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Date: Thu, 9 May 2024 11:34:31 -0700
From: Mayank Rana <quic_mrana@...cinc.com>
To: Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>,
        Krzysztof Wilczyński
	<kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, <johan+linaro@...nel.org>,
        <bmasney@...hat.com>, <djakov@...nel.org>
CC: <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <vireshk@...nel.org>, <quic_vbadigan@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <quic_parass@...cinc.com>, <krzysztof.kozlowski@...aro.org>,
        Bryan O'Donoghue
	<bryan.odonoghue@...aro.org>
Subject: Re: [PATCH v12 2/6] PCI: qcom: Add ICC bandwidth vote for CPU to PCIe
 path

Hi Krishna

On 4/26/2024 6:52 PM, Krishna chaitanya chundru wrote:
> To access the host controller registers of the host controller and the
> endpoint BAR/config space, the CPU-PCIe ICC (interconnect) path should
> be voted otherwise it may lead to NoC (Network on chip) timeout.
> We are surviving because of other driver voting 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 which is sufficient enough
> to keep the path active and is recommended by HW team.
> 
> During S2RAM (Suspend-to-RAM), the DBI access can happen very late (while
> disabling the boot CPU). So do not disable the CPU-PCIe interconnect path
> during S2RAM as that may lead to NoC error.
> 
> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> ---
>   drivers/pci/controller/dwc/pcie-qcom.c | 44 ++++++++++++++++++++++++++++++----
>   1 file changed, 40 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 14772edcf0d3..465d63b4be1c 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -245,6 +245,7 @@ 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;
> @@ -1409,6 +1410,9 @@ 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.
> @@ -1418,7 +1422,20 @@ 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 bandwidth for PCIe-MEM interconnect path: %d\n",
> +			ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Since the CPU-PCIe path is only used for activities like register
> +	 * access of the host controller and endpoint Config/BAR space access,
> +	 * HW team has recommended to use a minimal bandwidth of 1KBps just to
> +	 * keep the path active.
> +	 */
> +	ret = icc_set_bw(pcie->icc_cpu, 0, kBps_to_icc(1));
> +	if (ret) {
> +		dev_err(pci->dev, "Failed to set bandwidth for CPU-PCIe interconnect path: %d\n",
>   			ret);
Is it needed to undo icc_mem related bus bandwidth vote here ?
>   		return ret;
>   	}
> @@ -1448,7 +1465,7 @@ static void qcom_pcie_icc_update(struct qcom_pcie *pcie)
>   
>   	ret = icc_set_bw(pcie->icc_mem, 0, width * QCOM_PCIE_LINK_SPEED_TO_BW(speed));
>   	if (ret) {
> -		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
> +		dev_err(pci->dev, "Failed to set bandwidth for PCIe-MEM interconnect path: %d\n",
>   			ret);
>   	}
>   }