Re: [PATCH 4/5] PCI: qcom: Add link retention support

[Manivannan Sadhasivam]

On Fri, Jan 09, 2026 at 12:51:09PM +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 if driver doesn't want to do link training again.
> 
> 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 pp.link_retain and skip controller reset, PERST# toggling,
> and other post-init steps.
> 
> If there is a devicetree property to restrict PCIe data rate and lane
> width go with the normal execution instead of link retantion logic.
> 

Mention the properties here and also make it clear that the link will not be
retained if the values do not match bootloader programmed ones.

> Configure DBI and ATU base in this scenerio, since bootloader DBI & ATU
> base may differ from HLOS one. So use the DBI & ATU provided from the
> devicetree.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 50 ++++++++++++++++++++++++++++++++--
>  1 file changed, 47 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 9342f9c75f1c3017b55614069a7aa821a6fb8da7..bdd5bdb462c5f6814c8311be96411173456b6b14 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -259,12 +259,14 @@ 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 link retain from bootloader

s/"link retain"/"retaining link"

>    */
>  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_port {
> @@ -965,6 +967,35 @@ static int qcom_pcie_get_resources_2_7_0(struct qcom_pcie *pcie)
>  	return 0;
>  }
>  
> +static bool qcom_pcie_check_link_retain(struct qcom_pcie *pcie)
> +{
> +	u32 cap, speed, val, ltssm, 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);
> +
> +		if (pci->max_link_speed > 0 && speed < pci->max_link_speed)
> +			return false;
> +
> +		if (pci->num_lanes > 0 && width > pci->num_lanes)
> +			return false;

IIUC, these checks are in place to override the link retention if the users want
to change the lane/width count than what was already programmed by the
bootloader.

If so, please add comment on top of this helper to make it explicit.

> +
> +		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;
> @@ -983,6 +1014,14 @@ 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);
> +		if (pci->pp.link_retain) {
> +			dev_info(dev, "Enabling link retain\n");

"Retaining PCIe link"

- Mani

-- 
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