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Message-ID:
<AS8PR04MB8833807ECE928024892B73408CD5A@AS8PR04MB8833.eurprd04.prod.outlook.com>
Date: Fri, 21 Nov 2025 05:21:58 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Manivannan Sadhasivam <mani@...nel.org>, Shawn Lin
<shawn.lin@...k-chips.com>
CC: Frank Li <frank.li@....com>, Manivannan Sadhasivam
<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-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
"zhangsenchuan@...incomputing.com" <zhangsenchuan@...incomputing.com>
Subject: RE: [PATCH 2/2] PCI: dwc: Do not return failure from
dw_pcie_wait_for_link() if link is in Detect/Poll state
> -----Original Message-----
> From: Manivannan Sadhasivam <mani@...nel.org>
> Sent: 2025年11月20日 13:37
> To: Shawn Lin <shawn.lin@...k-chips.com>
> Cc: Hongxing Zhu <hongxing.zhu@....com>; Frank Li <frank.li@....com>;
> Manivannan Sadhasivam <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 2/2] PCI: dwc: Do not return failure from
> dw_pcie_wait_for_link() if link is in Detect/Poll state
>
> + Richard, Frank
>
> On Thu, Nov 20, 2025 at 09:13:24AM +0800, Shawn Lin wrote:
> > 在 2025/11/20 星期四 2:10, Manivannan Sadhasivam 写道:
> > > 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 and Poll 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() if the link is in Detect or Poll state 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 | 8 ++++++++
> > > 2 files changed, 13 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index 8fe3454f3b13..8c4845fd24aa 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -671,9 +671,11 @@ 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 c644216995f6..fe13c6b10ccb 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > @@ -651,6 +651,14 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
> > > }
> > > if (retries >= PCIE_LINK_WAIT_MAX_RETRIES) {
> > > + /*
> > > + * If the link is in Detect or Poll state, it indicates that no
> > > + * device is connected. So return success to allow the device to
> > > + * show up later.
> > > + */
> > > + if (dw_pcie_get_ltssm(pci) <= DW_PCIE_LTSSM_DETECT_WAIT)
> > > + return 0;
> >
> > I'm afraid this might not be true. If there is no devices connected or
> > the device connected without power supplied, it means there is no
> > far-end pull-up termination resistor from TX view of RC. TX pulse
> > detection signal from the RC side will not undergo voltage division,
> > and its LTSSM state machine will only toggle between
> > DW_PCIE_LTSSM_DETECT_QUIET and DW_PCIE_LTSSM_DETECT_ACT.
> >
>
> I must admit that I just inherited this check from dw_pcie_suspend_noirq().
> But I cross checked the PCIe base spec and it mentions clearly that the
> LTSSM will be in Detect.Quiet/Active states if no endpoint is detected i.e.,
> within the 1s timeout, the LTSSM should've transitioned back to these
> Detect states.
>
> I'm wondering why we are checking for Poll and other states in
> dw_pcie_suspend_noirq(). I believe the intention was to check for the
> presence of an endpoint or not.
>
> Richard, Frank, thoughts?
>
Hi Mani:
Yes, it is.
In my initial upstreaming patches, the intention to check this state is to
figure out that there is an endpoint device or not.
+ /* Skip PME_Turn_Off message if there is no endpoint connected */
+ if (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_WAIT) {
Best Regards
Richard Zhu
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்
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