Re: [PATCH v2 2/2] PCI: dwc: Do not return failure if link is in Detect.Quiet/Active states

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

On 12/18/2025 5:34 PM, Manivannan Sadhasivam via B4 Relay wrote:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
>
> dw_pcie_wait_for_link() API waits for the link to be up and returns failure
> if the link is not up within the 1 second interval. But if there was no
> device connected to the bus, then the link up failure would be expected.
> In that case, the callers might want to skip the failure in a hope that the
> link will be up later when a device gets connected.
>
> One of the callers, dw_pcie_host_init() is currently skipping the failure
> irrespective of the link state, in an assumption that the link may come up
> later. But this assumption is wrong, since LTSSM states other than
> Detect.Quiet and Detect.Active during link training phase are considered to
> be fatal and the link needs to be retrained.
>
> So to avoid callers making wrong assumptions, skip returning failure from
> dw_pcie_wait_for_link() only if the link is in Detect.Quiet or
> Detect.Active states after timeout and also check the return value of the
> API in dw_pcie_host_init().
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> ---
>   drivers/pci/controller/dwc/pcie-designware-host.c |  8 +++++---
>   drivers/pci/controller/dwc/pcie-designware.c      | 12 +++++++++++-
>   2 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 43d091128ef7..ef6d9ae6eddb 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -670,9 +670,11 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>   	 * If there is no Link Up IRQ, we should not bypass the delay
>   	 * because that would require users to manually rescan for devices.
>   	 */
> -	if (!pp->use_linkup_irq)
> -		/* Ignore errors, the link may come up later */
> -		dw_pcie_wait_for_link(pci);
> +	if (!pp->use_linkup_irq) {
> +		ret = dw_pcie_wait_for_link(pci);
> +		if (ret)
> +			goto err_stop_link;
> +	}
>   
>   	ret = pci_host_probe(bridge);
>   	if (ret)
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 75fc8b767fcc..b58baf26ce58 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -641,7 +641,7 @@ void dw_pcie_disable_atu(struct dw_pcie *pci, u32 dir, int index)
>   
>   int dw_pcie_wait_for_link(struct dw_pcie *pci)
>   {
> -	u32 offset, val;
> +	u32 offset, val, ltssm;
>   	int retries;
>   
>   	/* Check if the link is up or not */
> @@ -653,6 +653,16 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
>   	}
>   
>   	if (retries >= PCIE_LINK_WAIT_MAX_RETRIES) {
> +		/*
> +		 * If the link is in Detect.Quiet or Detect.Active state, it
> +		 * indicates that no device is detected. So return success to
> +		 * allow the device to show up later.
> +		 */
> +		ltssm = dw_pcie_get_ltssm(pci);
> +		if (ltssm == DW_PCIE_LTSSM_DETECT_QUIET ||
> +		    ltssm == DW_PCIE_LTSSM_DETECT_ACT)
> +			return 0;
> +
>   		dev_info(pci->dev, "Phy link never came up\n");
Can you move this print above, as this print is useful for the user to 
know that, link is not up yet.

- Krishna Chaitanya.
>   		return -ETIMEDOUT;
>   	}
>