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: <7a72f708-3f1a-421d-9299-e4ebb112f1ea@oss.qualcomm.com>
Date: Thu, 18 Dec 2025 18:58:55 +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 6:30 PM, Manivannan Sadhasivam wrote:
> On Thu, Dec 18, 2025 at 06:26:12PM +0530, Krishna Chaitanya Chundru wrote:
>>
>> 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.
>>
> Users won't grep the dmesg log to check whether the device is connected to the
> bus or not. They will use lspci.
ack.

- Krishna Chaitanya.
> - Mani
>