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

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Message-ID: <c4aedf62-633d-4871-9dfa-af021e9a8e42@oss.qualcomm.com>
Date: Thu, 18 Dec 2025 18:26:12 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: manivannan.sadhasivam@....qualcomm.com, Jingoo Han
 <jingoohan1@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        vincent.guittot@...aro.org, zhangsenchuan@...incomputing.com
Subject: Re: [PATCH v2 2/2] PCI: dwc: Do not return failure if link is in
 Detect.Quiet/Active states



On 12/18/2025 6:16 PM, Manivannan Sadhasivam wrote:
> On Thu, Dec 18, 2025 at 05:57:30PM +0530, Krishna Chaitanya Chundru wrote:
>>
>> On 12/18/2025 5:34 PM, Manivannan Sadhasivam via B4 Relay wrote:
>>> From: Manivannan Sadhasivam <manivannan.sadhasivam@....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@....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.
>>
> If the device is not connected to the bus, what information does this log
> provide to the user?
Not every user is aware that device is not connected, at-least this log 
will give info
that there is no device connected.

- Krishna Chaitanya.
> - Mani
>