linux-kernel - Re: [PATCH v2] PCI: qcom: fix IPQ8074 Gen2 support

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Message-ID: <YrMspGTROJUFYQrN@hovoldconsulting.com>
Date:   Wed, 22 Jun 2022 16:52:20 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Robert Marko <robimarko@...il.com>, svarbanov@...sol.com,
        agross@...nel.org, bjorn.andersson@...aro.org,
        lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, p.zabel@...gutronix.de, jingoohan1@...il.com,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, johan+linaro@...nel.org
Subject: Re: [PATCH v2] PCI: qcom: fix IPQ8074 Gen2 support

On Wed, Jun 22, 2022 at 08:49:19AM +0200, Johan Hovold wrote:
> On Tue, Jun 21, 2022 at 03:32:11PM -0500, Bjorn Helgaas wrote:
> > On Tue, Jun 21, 2022 at 01:23:30PM +0200, Robert Marko wrote:
> > > IPQ8074 has one Gen2 and one Gen3 port, currently the Gen2 port will
> > > cause the system to hang as its using DBI registers in the .init
> > > and those are only accesible after phy_power_on().
> > 
> > Is the fact that IPQ8074 has both a Gen2 and a Gen3 port relevant to
> > this patch?  I don't see the connection.
> > 
> > I see that qcom_pcie_host_init() does:
> > 
> >   qcom_pcie_host_init
> >     pcie->cfg->ops->init(pcie)
> >     phy_power_on(pcie->phy)
> >     pcie->cfg->ops->post_init(pcie)
> > 
> > and that you're moving DBI register accesses from
> > qcom_pcie_init_2_3_3() to qcom_pcie_post_init_2_3_3().
> > 
> > But I also see DBI register accesses in other .init() functions:
> > 
> >   qcom_pcie_init_2_1_0
> >   qcom_pcie_init_1_0_0      (oddly out of order)
> >   qcom_pcie_init_2_3_2
> >   qcom_pcie_init_2_4_0
> > 
> > Why do these accesses not need to be moved?  I assume it's because
> > pcie->phy is an optional PHY and phy_power_on() does nothing on those
> > controllers?
> 
> At least the QMP PHY driver does not implement the PHY power_on op and
> instead fires everything up already at phy_init(). That may explain the
> difference in behaviour here.

That was due to a bug in -next which as since been fixed by commit

	5bef2838f1a0 ("phy: qcom-qmp: fix PCIe PHY support")

which again do all PHY init at phy_power_on() instead of at phy_init().

Note also that before commit cc1e06f033af ("phy: qcom: qmp: Use
power_on/off ops for PCIe") everything was done at init.

Johan