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Date: Thu, 9 Jun 2022 06:17:46 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Lucas Stach <l.stach@...gutronix.de>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"broonie@...nel.org" <broonie@...nel.org>,
"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
"jingoohan1@...il.com" <jingoohan1@...il.com>,
"festevam@...il.com" <festevam@...il.com>,
"francesco.dolcini@...adex.com" <francesco.dolcini@...adex.com>
CC: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kernel@...gutronix.de" <kernel@...gutronix.de>,
dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH v9 6/8] PCI: imx6: Disable clocks and regulators after
link is down
> -----Original Message-----
> From: Lucas Stach <l.stach@...gutronix.de>
> Sent: 2022年6月8日 15:35
> To: Hongxing Zhu <hongxing.zhu@....com>; bhelgaas@...gle.com;
> robh+dt@...nel.org; broonie@...nel.org; lorenzo.pieralisi@....com;
> jingoohan1@...il.com; festevam@...il.com;
> francesco.dolcini@...adex.com
> Cc: linux-pci@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; kernel@...gutronix.de; dl-linux-imx
> <linux-imx@....com>
> Subject: Re: [PATCH v9 6/8] PCI: imx6: Disable clocks and regulators after link is
> down
>
> Am Freitag, dem 06.05.2022 um 09:47 +0800 schrieb Richard Zhu:
> > Since i.MX PCIe doesn't support hot-plug, reduce power consumption as
> > much as possible by disabling clocks and regulators and returning
> > error when the link is down.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> > drivers/pci/controller/dwc/pci-imx6.c | 19 +++++++++++++++----
> > 1 file changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 3ce3993d5797..d122c12193a6 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -845,7 +845,9 @@ static int imx6_pcie_start_link(struct dw_pcie *pci)
> > /* Start LTSSM. */
> > imx6_pcie_ltssm_enable(dev);
> >
> > - dw_pcie_wait_for_link(pci);
> > + ret = dw_pcie_wait_for_link(pci);
> > + if (ret)
> > + goto err_out;
>
> This adds back error handling that has been intentionally removed in
> f81f095e8771 ("PCI: imx6: Allow to probe when dw_pcie_wait_for_link() fails").
> While I agree that disabling the clocks and regulators is the right thing to do
> when we don't manage to get a link, we should still allow the driver to probe,
> so please add a "ret = 0" to this newly added non-fatal error paths.
>
Thanks for your review comments.
There would be a long latency if the link is down and probe is finished
successfully.
Since the dw_pcie_wait_for_link() would be invoked twice in every driver probe
and resume operation later. Each dw_pcie_wait_for_link() would consume about
90,000*10 ~ 100,000*10 u-seconds. I'm afraid that such a long latency would
bring bad user experience.
Here are the logs when probe is allowed when PCIe link is down:
[ 55.045954][ T1835] imx6q-pcie 5f000000.pcie: PM: calling imx6_pcie_resume_noirq.742dfa074b40dca7ca925f0c49c905ec.cfi_jt+0x0/0x8 @ 1835, parent: bus@...00000
...
[ 56.074566][ T1835] imx6q-pcie 5f000000.pcie: Phy link never came up
[ 57.074816][ T1835] imx6q-pcie 5f000000.pcie: Phy link never came up
...
[ 57.182300][ T1835] imx6q-pcie 5f000000.pcie: PM: imx6_pcie_resume_noirq.742dfa074b40dca7ca925f0c49c905ec.cfi_jt+0x0/0x8 returned 0 after 2136334 usecs
[ 57.182347][ T1835] imx6q-pcie 5f010000.pcie: PM: calling imx6_pcie_resume_noirq.742dfa074b40dca7ca925f0c49c905ec.cfi_jt+0x0/0x8 @ 1835, parent: bus@...00000
...
[ 58.210584][ T1835] imx6q-pcie 5f010000.pcie: Phy link never came up
[ 59.210831][ T1835] imx6q-pcie 5f010000.pcie: Phy link never came up
...
[ 59.318313][ T1835] imx6q-pcie 5f010000.pcie: PM: imx6_pcie_resume_noirq.742dfa074b40dca7ca925f0c49c905ec.cfi_jt+0x0/0x8 returned 0 after 2135949 usecs
So, I'm prefer that it's better to let the probe failed when link is down.
How do you think about that?
> >
> > if (pci->link_gen == 2) {
> > /* Allow Gen2 mode after the link is up. */ @@ -876,12 +878,14
> @@
> > static int imx6_pcie_start_link(struct dw_pcie *pci)
> > ret = imx6_pcie_wait_for_speed_change(imx6_pcie);
> > if (ret) {
> > dev_err(dev, "Failed to bring link up!\n");
> > - goto err_reset_phy;
> > + goto err_out;
> > }
> > }
> >
> > /* Make sure link training is finished as well! */
> > - dw_pcie_wait_for_link(pci);
> > + ret = dw_pcie_wait_for_link(pci);
> > + if (ret)
> > + goto err_out;
> > } else {
> > dev_info(dev, "Link: Gen2 disabled\n");
> > }
> > @@ -890,11 +894,18 @@ static int imx6_pcie_start_link(struct dw_pcie
> *pci)
> > dev_info(dev, "Link up, Gen%i\n", tmp & PCI_EXP_LNKSTA_CLS);
> > return 0;
> >
> > -err_reset_phy:
> > +err_out:
> > dev_dbg(dev, "PHY DEBUG_R0=0x%08x DEBUG_R1=0x%08x\n",
> > dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG0),
> > dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG1));
> > imx6_pcie_reset_phy(imx6_pcie);
> > + imx6_pcie_clk_disable(imx6_pcie);
> > + if (imx6_pcie->phy != NULL) {
>
> Please use the more common if (imx6_pcie->phy) here.
>
Okay. Thanks.
Best Regards
Richard Zhu
> Regards,
> Lucas
>
> > + phy_power_off(imx6_pcie->phy);
> > + phy_exit(imx6_pcie->phy);
> > + }
> > + if (imx6_pcie->vpcie)
> > + regulator_disable(imx6_pcie->vpcie);
> > return ret;
> > }
> >
>
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