From: Francesco Dolcini <francesco.dolcini@toradex.com>
To: Hongxing Zhu <hongxing.zhu@nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>,
"bhelgaas@google.com" <bhelgaas@google.com>,
"robh+dt@kernel.org" <robh+dt@kernel.org>,
"broonie@kernel.org" <broonie@kernel.org>,
"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
"jingoohan1@gmail.com" <jingoohan1@gmail.com>,
"festevam@gmail.com" <festevam@gmail.com>,
"francesco.dolcini@toradex.com" <francesco.dolcini@toradex.com>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kernel@pengutronix.de" <kernel@pengutronix.de>,
dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH v9 6/8] PCI: imx6: Disable clocks and regulators after link is down
Date: Thu, 9 Jun 2022 09:53:05 +0200 [thread overview]
Message-ID: <20220609075305.GA20630@francesco-nb.int.toradex.com> (raw)
In-Reply-To: <AS8PR04MB86763AE6FF5BABE3EBED833B8CA79@AS8PR04MB8676.eurprd04.prod.outlook.com>
On Thu, Jun 09, 2022 at 06:17:46AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Lucas Stach <l.stach@pengutronix.de>
> > Sent: 2022年6月8日 15:35
> > To: Hongxing Zhu <hongxing.zhu@nxp.com>; bhelgaas@google.com;
> > robh+dt@kernel.org; broonie@kernel.org; lorenzo.pieralisi@arm.com;
> > jingoohan1@gmail.com; festevam@gmail.com;
> > francesco.dolcini@toradex.com
> > Cc: linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> > linux-kernel@vger.kernel.org; kernel@pengutronix.de; dl-linux-imx
> > <linux-imx@nxp.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@nxp.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@5f000000
> ...
> [ 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@5f000000
> ...
> [ 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?
I think that recently Bjorn mentioned some concern with this approach,
and I agree with him.
I think that the probe of the PCIe root port should not fail if the link
is down.
What is the reason for such a long wait in dw_pcie_wait_for_link()? Is
this slowing down the resume process as a whole? Why called twice? (I'm
not familiar with that part of the code)
Francesco
next prev parent reply other threads:[~2022-06-09 7:55 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-06 1:47 [PATCH v9 0/8] PCI: imx6: refine codes and add compliance tests mode support Richard Zhu
2022-05-06 1:47 ` [PATCH v9 1/8] PCI: imx6: Encapsulate the clock enable into one standalone function Richard Zhu
2022-06-08 18:51 ` Bjorn Helgaas
2022-06-09 6:18 ` Hongxing Zhu
2022-05-06 1:47 ` [PATCH v9 2/8] PCI: imx6: Add the error propagation from host_init Richard Zhu
2022-06-08 18:53 ` Bjorn Helgaas
2022-06-09 6:19 ` Hongxing Zhu
2022-05-06 1:47 ` [PATCH v9 3/8] PCI: imx6: Move imx6_pcie_clk_disable() earlier Richard Zhu
2022-06-08 7:14 ` Lucas Stach
2022-05-06 1:47 ` [PATCH v9 4/8] PCI: imx6: Disable iMX6QDL PCIe REF clock when disable PCIe clocks Richard Zhu
2022-06-08 7:18 ` Lucas Stach
2022-05-06 1:47 ` [PATCH v9 5/8] PCI: imx6: Refine the regulator usage Richard Zhu
2022-06-08 7:26 ` Lucas Stach
2022-06-09 6:17 ` Hongxing Zhu
2022-06-09 7:47 ` Lucas Stach
2022-06-09 7:54 ` Hongxing Zhu
2022-06-08 18:54 ` Bjorn Helgaas
2022-06-09 6:19 ` Hongxing Zhu
2022-06-09 17:20 ` Bjorn Helgaas
2022-06-10 7:09 ` Hongxing Zhu
2022-05-06 1:47 ` [PATCH v9 6/8] PCI: imx6: Disable clocks and regulators after link is down Richard Zhu
2022-06-08 7:35 ` Lucas Stach
2022-06-09 6:17 ` Hongxing Zhu
2022-06-09 7:53 ` Francesco Dolcini [this message]
2022-06-09 8:36 ` Hongxing Zhu
2022-06-09 7:55 ` Lucas Stach
2022-06-09 8:30 ` Hongxing Zhu
2022-05-06 1:47 ` [PATCH v9 7/8] PCI: imx6: Move the phy driver callbacks to the proper places Richard Zhu
2022-06-08 7:44 ` Lucas Stach
2022-06-09 6:18 ` Hongxing Zhu
2022-06-08 18:57 ` Bjorn Helgaas
2022-06-09 6:20 ` Hongxing Zhu
2022-06-09 16:25 ` Bjorn Helgaas
2022-06-10 6:51 ` Hongxing Zhu
2022-05-06 1:47 ` [PATCH v9 8/8] PCI: imx6: Add compliance tests mode support Richard Zhu
2022-06-08 7:48 ` Lucas Stach
2022-06-09 6:18 ` Hongxing Zhu
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