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: <h65q3cilodzw3htdpdu66cijokigz6grlw4eol4jbyiodrqy4m@jcvp6vigeo5s>
Date: Thu, 18 Dec 2025 18:25:24 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Shawn Lin <shawn.lin@...k-chips.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 08:45:15PM +0800, Shawn Lin wrote:
> 在 2025/12/18 星期四 20:04, Manivannan Sadhasivam via B4 Relay 写道:
> > 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;
> 
> By looking more closely, this changes the behaviour of pcie-tegra194.c
> which relies on it in tegra_pcie_dw_start_link() to do some retries.
> 
> pcie-intel-gw.c/pci-imx6.c also continue to do some setups in this case,
> not sure if it's safe.
> 

Hmm, I agree. I did check the callers during v1, but fail to notice pci-imx6
which writes to LNKCAP and PCIE_LINK_WIDTH_SPEED_CONTROL registers after
success.

To be on the safe side, dw_pcie_wait_for_link() should return -ENODEV if the
device is not found and the callers can check for this errno and skip the
failure.

- Mani

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