linux-kernel - Re: [PATCH 2/2] PCI: imx: Initial imx7d pm support

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Date:   Wed, 4 Jul 2018 17:37:23 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Leonard Crestez <leonard.crestez@....com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        Richard Zhu <hongxing.zhu@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
        Abel Vesa <abel.vesa@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Anson Huang <anson.huang@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 2/2] PCI: imx: Initial imx7d pm support

On Tue, Jul 03, 2018 at 10:42:08AM +0200, Lucas Stach wrote:
> Am Montag, den 02.07.2018, 17:18 +0000 schrieb Leonard Crestez:
> > On Fri, 2018-06-08 at 16:33 +0200, Lucas Stach wrote:
> > > Am Dienstag, den 29.05.2018, 22:39 +0300 schrieb Leonard Crestez:
> > > > On imx7d the phy is turned off in suspend and must be reset on resume.
> > > > Right now lspci -v fails after a suspend/resume cycle, fix this by
> > > > adding minimal suspend/resume code from the nxp vendor tree.
> > > > 
> > > > This is currently only enabled for imx7 but the same sequence can be
> > > > applied to other imx pcie variants.
> > > > +#ifdef CONFIG_PM_SLEEP
> > > > +static int imx6_pcie_suspend_noirq(struct device *dev)
> > > > +{
> > > > > > > +	struct imx6_pcie *imx6_pcie = dev_get_drvdata(dev);
> > > > +
> > > > +	if (imx6_pcie->variant == IMX7D) {
> > > 
> > > Instead of this large indented block, please just have an early return
> > > at the start of this function, like:
> > > 
> > > if (imx6_pcie->variant != IMX7D)
> > > 	return 0;
> > > 
> > > Same for the resume function.
> > 
> > OK. The resume sequence is mostly the same for all SOCs where it
> > applies.
> > 
> > > > +static int imx6_pcie_resume_noirq(struct device *dev)
> > > > +{
> > > > > > > +	int ret = 0;
> > > > > > > +	struct imx6_pcie *imx6_pcie = dev_get_drvdata(dev);
> > > > > > > +	struct pcie_port *pp = &imx6_pcie->pci->pp;
> > > > 
> > > > +
> > > > > > > +	if (imx6_pcie->variant == IMX7D) {
> > > > +		imx6_pcie_ltssm_disable(dev);
> > > 
> > > The LTSSM disable seems misplaced here. I would have expected it to be
> > > in the suspend function.
> > 
> > This is a requirement for reinitializing the core: LTSSM needs to be
> > turned off during initialization.
> 
> If you disable LTSSM during suspend, it should be off when entering
> this resume function, no?
> 
> > > > +		/*
> > > > > > > +		 * controller maybe turn off, re-configure again
> > > > > > > +		 */
> > > > > > > +		dw_pcie_setup_rc(pp);
> > > > +
> > > > > > > +		imx6_pcie_ltssm_enable(dev);
> > > > +
> > > > > > > +		ret = imx6_pcie_wait_for_link(imx6_pcie);
> > > > > > > +		if (ret < 0)
> > > > +			pr_info("pcie link is down after resume.\n");
> > > 
> > > If the PHY has been powered down and LTSSM stopped I guess we need to
> > > do the full imx6_pcie_establish_link() dance again here to reliably re-
> > > establish the link. The above seems unsafe.
> > 
> > What imx6_pcie_establish_link does additionally is some workaround for
> > link gen detection. I agree that it should be included.
> > 
> > This would make resume mostly the same as imx_pcie_host_init except for
> > dw_pcie_msi_init; that needs to be saved/restored separately.
> 
> Right, so maybe we can even cut down on lines of code by splitting and
> reusing existing functions.
> 
> > 
> > Another issue that should be discussed here is that on 6sx and 7d the
> > gpc PCIE power domain is not defined correctly: the PCIE block is in
> > the DISPMIX domain on both SOCs and it is only PCIE_PHY which has a
> > separate power domain.
> > 
> > This matters: enabling power-gating for displays will break pcie if
> > this relationship is not taken into account. Here are some options:
> > 
> > 1) Make &pd_pcie a child of &pd_disp by hacking into gpc probe
> > functions and calling pm_genpd_add_subdomain. Not very nice.
> > 
> > 2) Support nesting PGCs in GPC code? Lots of code and still an
> > incorrect representation of hardware.
> > 
> > 3) Set power-domains = <&pd_disp> and enable runtime PM on &pd_pcie?
> > 
> > 4) Add separate devices for the pcie-phy. These would be mostly empty
> > but still different, for example on imx6sx the PHY is not even
> > accessible on the bus but only though PCIE registers.
> 
> 5) Take a look at the linux-pm list. ;) The power domain framework has
> just gained support for multiple power domains per device. I think that
>  is the right solution for this, as like you mentioned the PHY isn't
> really a separate block on i.MX6, but part of the PCIe controller
> device.

>From the discussion I take this as there is going to be a v2 so
I will mark this as Changes Requested, please let me know if that's
a problem.

Thanks,
Lorenzo