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Message-ID: <ZzOCi1RKvB9Siy1y@lizhi-Precision-Tower-5810>
Date: Tue, 12 Nov 2024 11:30:03 -0500
From: Frank Li <Frank.li@....com>
To: Hongxing Zhu <hongxing.zhu@....com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
Bjorn Helgaas <helgaas@...nel.org>,
"jingoohan1@...il.com" <jingoohan1@...il.com>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
"kw@...ux.com" <kw@...ux.com>, "robh@...nel.org" <robh@...nel.org>,
"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
"kernel@...gutronix.de" <kernel@...gutronix.de>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] PCI: dwc: Clean up some unnecessary codes in
dw_pcie_suspend_noirq()
On Tue, Nov 12, 2024 at 09:15:25AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > Sent: 2024年11月12日 16:02
> > To: Frank Li <frank.li@....com>
> > Cc: Bjorn Helgaas <helgaas@...nel.org>; Hongxing Zhu
> > <hongxing.zhu@....com>; jingoohan1@...il.com; bhelgaas@...gle.com;
> > lpieralisi@...nel.org; kw@...ux.com; robh@...nel.org; imx@...ts.linux.dev;
> > kernel@...gutronix.de; linux-pci@...r.kernel.org;
> > linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH v1] PCI: dwc: Clean up some unnecessary codes in
> > dw_pcie_suspend_noirq()
> >
> > On Mon, Nov 11, 2024 at 12:42:50PM -0500, Frank Li wrote:
> > > On Mon, Nov 11, 2024 at 11:39:02AM +0530, Manivannan Sadhasivam
> > wrote:
> > > > On Thu, Nov 07, 2024 at 06:24:25PM -0600, Bjorn Helgaas wrote:
> > > > > On Thu, Nov 07, 2024 at 11:13:34AM +0000, Manivannan Sadhasivam
> > wrote:
> > > > > > On Thu, Nov 07, 2024 at 04:44:55PM +0800, Richard Zhu wrote:
> > > > > > > Before sending PME_TURN_OFF, don't test the LTSSM stat. Since
> > > > > > > it's safe to send PME_TURN_OFF message regardless of whether
> > > > > > > the link is up or down. So, there would be no need to test the
> > > > > > > LTSSM stat before sending PME_TURN_OFF message.
> > > > > >
> > > > > > What is the incentive to send PME_Turn_Off when link is not up?
> > > > >
> > > > > There's no need to send PME_Turn_Off when link is not up.
> > > > >
> > > > > But a link-up check is inherently racy because the link may go
> > > > > down between the check and the PME_Turn_Off. Since it's
> > > > > impossible for software to guarantee the link is up, the Root Port
> > > > > should be able to tolerate attempts to send PME_Turn_Off when the link
> > is down.
> > > > >
> > > > > So IMO there's no need to check whether the link is up, and
> > > > > checking gives the misleading impression that "we know the link is
> > > > > up and therefore sending PME_Turn_Off is safe."
> > > > >
> > > >
> > > > I agree that the check is racy (not sure if there is a better way to
> > > > avoid that), but if you send the PME_Turn_Off unconditionally, then
> > > > it will result in
> > > > L23 Ready timeout and users will see the error message.
> > > >
> > > > > > > Remove the L2 poll too, after the PME_TURN_OFF message is sent
> > > > > > > out. Because the re-initialization would be done in
> > > > > > > dw_pcie_resume_noirq().
> > > > > >
> > > > > > As Krishna explained, host needs to wait until the endpoint acks
> > > > > > the message (just to give it some time to do cleanups). Then
> > > > > > only the host can initiate D3Cold. It matters when the device supports
> > L2.
> > > > >
> > > > > The important thing here is to be clear about the *reason* to poll
> > > > > for
> > > > > L2 and the *event* that must wait for L2.
> > > > >
> > > > > I don't have any DesignWare specs, but when
> > > > > dw_pcie_suspend_noirq() waits for DW_PCIE_LTSSM_L2_IDLE, I think
> > > > > what we're doing is waiting for the link to be in the L2/L3 Ready
> > > > > pseudo-state (PCIe r6.0, sec 5.2, fig 5-1).
> > > > >
> > > > > L2 and L3 are states where main power to the downstream component
> > > > > is off, i.e., the component is in D3cold (r6.0, sec 5.3.2), so
> > > > > there is no link in those states.
> > > > >
> > > > > The PME_Turn_Off handshake is part of the process to put the
> > > > > downstream component in D3cold. I think the reason for this
> > > > > handshake is to allow an orderly shutdown of that component before
> > > > > main power is removed.
> > > > >
> > > > > When the downstream component receives PME_Turn_Off, it will stop
> > > > > scheduling new TLPs, but it may already have TLPs scheduled but
> > > > > not yet sent. If power were removed immediately, they would be
> > > > > lost. My understanding is that the link will not enter L2/L3
> > > > > Ready until the components on both ends have completed whatever
> > > > > needs to be done with those TLPs. (This is based on the L2/L3
> > > > > discussion in the Mindshare PCIe book; I haven't found clear spec
> > > > > citations for all of it.)
> > > > >
> > > > > I think waiting for L2/L3 Ready is to keep us from turning off
> > > > > main power when the components are still trying to dispose of those
> > TLPs.
> > > > >
> > > >
> > > > Not just disposing TLPs as per the spec, most endpoints also need to
> > > > reset their state machine as well (if there is a way for the
> > > > endpoint sw to delay sending
> > > > L23 Ready).
> > > >
> > > > > So I think every controller that turns off main power needs to
> > > > > wait for L2/L3 Ready.
> > > > >
> > > > > There's also a requirement that software wait at least 100 ns
> > > > > after
> > > > > L2/L3 Ready before turning off refclock and main power (sec
> > > > > 5.3.3.2.1).
> > > > >
> > > >
> > > > Right. Usually, the delay after PERST# assert would make sure this,
> > > > but in layerscape driver (user of dw_pcie_suspend_noirq) I don't see
> > > > power/refclk removal.
> > > >
> > > > Richard Zhu/Frank, thoughts?
> > >
> > > Generally, power/refclk remove when system enter sleep state. There is
> > > signal "suspend_request_b", which connect to PMIC. After CPU trigger
> > > this signnal, PMIC will turn off (pre fused) some power rail.
> > >
> > > Refclk(come from SOC chip), OSC will be shutdown when send out
> > > "suspend_request_b".
> > >
> >
> > Thanks for clarifying! Then it would be better to add the 100ns delay after
> > receiving the L23 Ready message from endpoint.
> Okay.
> How about the following changes?
> - Before dump error message, make sure link is up.
> - Add 1us delay after L2/L3 Ready is received.
>
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -940,9 +940,16 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
> PCIE_PME_TO_L2_TIMEOUT_US/10,
> PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
My means change
val == DW_PCIE_LTSSM_L2_IDLE || val == XXX
XXX should be one of below value when linkdown, Maybe S_DISABLED or
S_DETECT_QUIET
00_0000b - S_DETECT_QUIET
00_0001b - S_DETECT_ACT
00_0010b - S_POLL_ACTIVE
00_0011b - S_POLL_COMPLIANCE
00_0100b - S_POLL_CONFIG
00_0101b - S_PRE_DETECT_QUIET
00_0110b - S_DETECT_WAIT
00_0111b - S_CFG_LINKWD_START
00_1000b - S_CFG_LINKWD_ACEPT
00_1001b - S_CFG_LANENUM_WAI
00_1010b - S_CFG_LANENUM_ACEPT
00_1011b - S_CFG_COMPLETE
00_1100b - S_CFG_IDLE
00_1101b - S_RCVRY_LOCK
00_1110b - S_RCVRY_SPEED
00_1111b - S_RCVRY_RCVRCFG
01_0000b - S_RCVRY_IDLE
01_0001b - S_L0
01_0010b - S_L0S
01_0011b - S_L123_SEND_EIDLE
01_0100b - S_L1_IDLE
01_0101b - S_L2_IDLE
01_0110b - S_L2_WAKE
01_0111b - S_DISABLED_ENTRY
01_1000b - S_DISABLED_IDLE
01_1001b - S_DISABLED
01_1010b - S_LPBK_ENTRY
01_1011b - S_LPBK_ACTIVE
01_1100b - S_LPBK_EXIT
01_1101b - S_LPBK_EXIT_TIMEOUT
01_1110b - S_HOT_RESET_ENTRY
01_1111b - S_HOT_RESET
10_0000b - S_RCVRY_EQ0
10_0001b - S_RCVRY_EQ1
10_0010b - S_RCVRY_EQ2
10_0011b - S_RCVRY_EQ3
> - if (ret) {
> + if (ret && dw_pcie_link_up(pci)) {
> dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
> return ret;
> + } else {
> + /*
> + * Refer to r6.0, sec 5.3.3.2.1, software should wait at
> + * least 100ns after L2/L3 Ready before turning off
> + * refclock and main power.
> + */
> + udelay(1);
>
> Best Regards
> Richard Zhu
> >
> > - Mani
> >
> > --
> > மணிவண்ணன் சதாசிவம்
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