linux-kernel - Re: [PATCH v4 9/9] PCI: dwc: support missing PCIe device on resume

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Message-ID: <dc230a62-bd31-450a-9acd-fa654f694b3a@oss.qualcomm.com>
Date: Thu, 30 Oct 2025 11:07:19 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Sebastian Reichel <sebastian.reichel@...labora.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Heiko Stuebner <heiko@...ech.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jingoo Han <jingoohan1@...il.com>,
        Shawn Lin <shawn.lin@...k-chips.com>
Cc: linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v4 9/9] PCI: dwc: support missing PCIe device on resume


On 10/29/2025 11:26 PM, Sebastian Reichel wrote:
> When dw_pcie_resume_noirq() is called for a PCIe root complex for a PCIe
> slot with no device plugged on Rockchip RK3576, dw_pcie_wait_for_link()
> will return -ETIMEDOUT. During probe time this does not happen, since
> the platform sets 'use_linkup_irq'.
>
> This adds the same logic from dw_pcie_host_init() to the PM resume
> function to avoid the problem.
>
> Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
> ---
>   drivers/pci/controller/dwc/pcie-designware-host.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index e92513c5bda5..f25f1c136900 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -1215,9 +1215,16 @@ int dw_pcie_resume_noirq(struct dw_pcie *pci)
>   	if (ret)
>   		return ret;
>   
> -	ret = dw_pcie_wait_for_link(pci);
> -	if (ret)
> -		return ret;
> +	/*
> +	 * Note: Skip the link up delay only when a Link Up IRQ is present.
> +	 * If there is no Link Up IRQ, we should not bypass the delay
> +	 * because that would require users to manually rescan for devices.
> +	 */

In the resume scenario, we should explicitly wait for the link to be up, 
there is no IRQ support at this resume phase
and secondly after controller resume pm framework will start resuming 
the bridges & endpoints. what happens
if the link is not up by the time endpoint is resume is called. And 
entire save & restore states might also gets messed up.
There will be no way to recover from this.

- Krishna Chaitanya.

> +	if (!pci->pp.use_linkup_irq) {
> +		ret = dw_pcie_wait_for_link(pci);
> +		if (ret)
> +			return ret;
> +	}
>   
>   	return ret;
>   }
>