[PATCH v3 3/4] PCI: qcom: Add link retention support

[Manivannan Sadhasivam]

On Thu, Jul 09, 2026 at 12:05:18PM +0530, Krishna Chaitanya Chundru wrote:
> Some platforms keep the PCIe link active across bootloader and kernel
> handoff. Reinitializing the controller and toggling PERST# in such cases is
> unnecessary when the driver does not need to retrain the link.
> 
> Introduce link_retain in both qcom_pcie_cfg and qcom_pcie to indicate when
> link retention is supported. During initialization, check the LTSSM state;
> if the link is already in L0 or L1 idle and LTSSM is enabled, set
> link_retain and skip controller reset, PERST# toggling, and other post-
> init steps.
> 
> The max-link-speed and num-lanes properties in Device Tree cap the link's
> maximum capability. Retrain the link if the controller's max link speed or
> width exceeds the Device Tree cap, unless the currently negotiated speed
> or width is already within that cap, in which case the existing link can
> still be retained.
> 
> Configure the DBI and ATU base addresses in the retention path, since the
> bootloader may use different base addresses than those provided by the
> device tree.
> 

Where is this base address change?

> Set l1ss_support in the retention path as well, since it is otherwise only
> set later in the normal init flow which is skipped when the link is
> retained.
> 
> Tested-by: Qiang Yu <qiang.yu at oss.qualcomm.com>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru at oss.qualcomm.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.h |  1 +
>  drivers/pci/controller/dwc/pcie-qcom.c       | 68 ++++++++++++++++++++++++++--
>  2 files changed, 66 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index de4b245b1758..0c98b914eb52 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -471,6 +471,7 @@ struct dw_pcie_rp {
>  	bool			native_ecam;
>  	bool                    skip_l23_ready;
>  	bool			skip_pwrctrl_off;
> +	bool			link_retain;
>  };
>  
>  struct dw_pcie_ep_ops {
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 9ca620d4746a..77d2d989e9da 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -260,12 +260,14 @@ struct qcom_pcie_ops {
>    * @override_no_snoop: Override NO_SNOOP attribute in TLP to enable cache
>    * snooping
>    * @firmware_managed: Set if the Root Complex is firmware managed
> +  * @link_retain: Set if controller supports retaining link from bootloader
>    */
>  struct qcom_pcie_cfg {
>  	const struct qcom_pcie_ops *ops;
>  	bool override_no_snoop;
>  	bool firmware_managed;
>  	bool no_l0s;
> +	bool link_retain;
>  };
>  
>  struct qcom_pcie_perst {
> @@ -996,6 +998,50 @@ static int qcom_pcie_get_resources_2_7_0(struct qcom_pcie *pcie)
>  	return 0;
>  }
>  
> +/*
> + * Determine whether the link established by the bootloader can be reused.
> + *
> + * The max-link-speed and num-lanes specified in Device Tree are meant to cap
> + * the link's maximum capability. Retrain the link if the controller's max
> + * link speed/width exceeds the Device Tree cap, unless the currently
> + * negotiated speed/width is already within that cap, in which case the
> + * existing link can be retained as-is.
> + */
> +static bool qcom_pcie_check_link_retain(struct qcom_pcie *pcie)
> +{
> +	u32 cap, speed, cur_speed, val, ltssm, width, cur_width;
> +	struct dw_pcie *pci = pcie->pci;
> +	u8 offset;
> +
> +	val = readl(pcie->parf + PARF_LTSSM);
> +	ltssm = val & 0x1f;
> +	if ((val & LTSSM_EN) &&
> +	    (ltssm == DW_PCIE_LTSSM_L0 || ltssm == DW_PCIE_LTSSM_L1_IDLE)) {
> +		qcom_pcie_configure_dbi_atu_base(pcie);
> +
> +		offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +		cap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
> +		speed = FIELD_GET(PCI_EXP_LNKCAP_SLS, cap);
> +		width = dw_pcie_link_get_max_link_width(pci);
> +
> +		val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
> +		cur_speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, val);
> +		cur_width = FIELD_GET(PCI_EXP_LNKSTA_NLW, val);
> +
> +		if (pci->max_link_speed > 0 && speed > pci->max_link_speed &&
> +		    cur_speed > pci->max_link_speed)
> +			return false;
> +
> +		if (pci->num_lanes > 0 && width > pci->num_lanes &&
> +		    cur_width > pci->num_lanes)
> +			return false;
> +
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>  static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
>  {
>  	struct qcom_pcie_resources_2_7_0 *res = &pcie->res.v2_7_0;
> @@ -1014,6 +1060,15 @@ static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
>  	if (ret < 0)
>  		goto err_disable_regulators;
>  
> +	if (pcie->cfg->link_retain) {
> +		pci->pp.link_retain = qcom_pcie_check_link_retain(pcie);
> +		pci->l1ss_support = true;
> +		if (pci->pp.link_retain) {
> +			dev_info(dev, "Retaining PCIe link\n");
> +			return 0;
> +		}
> +	}
> +
>  	ret = reset_control_assert(res->rst);
>  	if (ret) {
>  		dev_err(dev, "reset assert failed (%d)\n", ret);
> @@ -1074,6 +1129,9 @@ static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
>  {
>  	const struct qcom_pcie_cfg *pcie_cfg = pcie->cfg;
>  
> +	if (pcie->pci->pp.link_retain)
> +		return 0;
> +
>  	if (pcie_cfg->override_no_snoop)
>  		writel(WR_NO_SNOOP_OVERRIDE_EN | RD_NO_SNOOP_OVERRIDE_EN,
>  				pcie->parf + PARF_NO_SNOOP_OVERRIDE);
> @@ -1364,12 +1422,13 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
>  	struct qcom_pcie *pcie = to_qcom_pcie(pci);
>  	int ret;
>  
> -	qcom_pcie_perst_assert(pcie);
> -

This is problematic. Most of the init callbacks do operations like reset the
PHY, enable clocks... If those operations affect the link state and the device
is not reset using PERST#, it will cause the device to crash.

- Mani

-- 
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