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

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Message-ID: <YrK7b1GaEMuANGtR@hovoldconsulting.com>
Date:   Wed, 22 Jun 2022 08:49:19 +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 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.

Johan