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: <bawi2oioatfrmxuwd26xlvytmtuo2mhf3yunbwrzam22y57wvm@3l4hdbzjjske>
Date: Thu, 18 Dec 2025 18:30:08 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
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 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.

- Mani

-- 
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