Re: [PATCH v2 2/2] PCI: qcom: Add basic interconnect support

[Georgi Djakov <djakov@kernel.org>]

Thanks for the patches, Johan!

On 21.10.22 9:46, Johan Hovold wrote:
> On Qualcomm platforms like SC8280XP and SA8540P, interconnect bandwidth
> must be requested before enabling interconnect clocks.
> 
> Add basic support for managing an optional "pcie-mem" interconnect path
> by setting a low constraint before enabling clocks and updating it after
> the link is up.
> 
> Note that it is not possible for a controller driver to set anything but
> a maximum peak bandwidth as expected average bandwidth will vary with
> use case and actual use (and power policy?). This very much remains an
> unresolved problem with the interconnect framework.
> 
> Also note that no constraint is set for the SC8280XP/SA8540P "cpu-pcie"
> path for now as it is not clear what an appropriate constraint would be
> (and the system does not crash when left unspecified).
> 
> Fixes: 70574511f3fc ("PCI: qcom: Add support for SC8280XP")
> Reviewed-by: Brian Masney <bmasney@redhat.com>
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>

Acked-by: Georgi Djakov <djakov@kernel.org>

Also CC-ing Stan's new e-mail address.

Thanks,
Georgi

> ---
>   drivers/pci/controller/dwc/pcie-qcom.c | 76 ++++++++++++++++++++++++++
>   1 file changed, 76 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 7db94a22238d..0c13f976626f 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -12,6 +12,7 @@
>   #include <linux/crc8.h>
>   #include <linux/delay.h>
>   #include <linux/gpio/consumer.h>
> +#include <linux/interconnect.h>
>   #include <linux/interrupt.h>
>   #include <linux/io.h>
>   #include <linux/iopoll.h>
> @@ -224,6 +225,7 @@ struct qcom_pcie {
>   	union qcom_pcie_resources res;
>   	struct phy *phy;
>   	struct gpio_desc *reset;
> +	struct icc_path *icc_mem;
>   	const struct qcom_pcie_cfg *cfg;
>   };
>   
> @@ -1644,6 +1646,74 @@ static const struct dw_pcie_ops dw_pcie_ops = {
>   	.start_link = qcom_pcie_start_link,
>   };
>   
> +static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
> +{
> +	struct dw_pcie *pci = pcie->pci;
> +	int ret;
> +
> +	pcie->icc_mem = devm_of_icc_get(pci->dev, "pcie-mem");
> +	if (IS_ERR(pcie->icc_mem)) {
> +		ret = PTR_ERR(pcie->icc_mem);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Some Qualcomm platforms require interconnect bandwidth constraints
> +	 * to be set before enabling interconnect clocks.
> +	 *
> +	 * Set an initial peak bandwidth corresponding to single-lane Gen 1
> +	 * for the pcie-mem path.
> +	 */
> +	ret = icc_set_bw(pcie->icc_mem, 0, MBps_to_icc(250));
> +	if (ret) {
> +		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
> +			ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void qcom_pcie_icc_update(struct qcom_pcie *pcie)
> +{
> +	struct dw_pcie *pci = pcie->pci;
> +	u32 offset, status, bw;
> +	int speed, width;
> +	int ret;
> +
> +	if (!pcie->icc_mem)
> +		return;
> +
> +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	status = readw(pci->dbi_base + offset + PCI_EXP_LNKSTA);
> +
> +	/* Only update constraints if link is up. */
> +	if (!(status & PCI_EXP_LNKSTA_DLLLA))
> +		return;
> +
> +	speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, status);
> +	width = FIELD_GET(PCI_EXP_LNKSTA_NLW, status);
> +
> +	switch (speed) {
> +	case 1:
> +		bw = MBps_to_icc(250);
> +		break;
> +	case 2:
> +		bw = MBps_to_icc(500);
> +		break;
> +	default:
> +	case 3:
> +		bw = MBps_to_icc(985);
> +		break;
> +	}
> +
> +	ret = icc_set_bw(pcie->icc_mem, 0, width * bw);
> +	if (ret) {
> +		dev_err(pci->dev, "failed to set interconnect bandwidth: %d\n",
> +			ret);
> +	}
> +}
> +
>   static int qcom_pcie_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> @@ -1704,6 +1774,10 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>   		goto err_pm_runtime_put;
>   	}
>   
> +	ret = qcom_pcie_icc_init(pcie);
> +	if (ret)
> +		goto err_pm_runtime_put;
> +
>   	ret = pcie->cfg->ops->get_resources(pcie);
>   	if (ret)
>   		goto err_pm_runtime_put;
> @@ -1722,6 +1796,8 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>   		goto err_phy_exit;
>   	}
>   
> +	qcom_pcie_icc_update(pcie);
> +
>   	return 0;
>   
>   err_phy_exit: