linux-kernel - Re: [PATCH v7 1/5] PCI: qcom: Add system suspend and resume support

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Message-ID: <20221013004444.GA3135316@bhelgaas>
Date:   Wed, 12 Oct 2022 19:44:44 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc:     linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mka@...omium.org,
        quic_vbadigan@...cinc.com, quic_hemantk@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_ramkri@...cinc.com, manivannan.sadhasivam@...aro.org,
        swboyd@...omium.org, dmitry.baryshkov@...aro.org,
        svarbanov@...sol.com, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...ainline.org, lpieralisi@...nel.org,
        robh@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        linux-phy@...ts.infradead.org, vkoul@...nel.org, kishon@...com,
        mturquette@...libre.com, linux-clk@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org,
        Marc Zyngier <maz@...nel.org>,
        Kevin Rowland <kevin.p.rowland@...il.com>
Subject: Re: [PATCH v7 1/5] PCI: qcom: Add system suspend and resume support

[+cc Marc, Kevin]

On Wed, Oct 12, 2022 at 07:36:52PM +0530, Krishna Chaitanya Chundru wrote:
> On 10/6/2022 2:43 AM, Bjorn Helgaas wrote:

[I'm declaring quote text bankruptcy and dropping the huge wall of
text.  The IRQ affinity change you mention seems to be the critical
issue :)]

> > The PCIe spec clearly envisions Refclk being turned off
> > (sec 5.5.3.3.1) and PHYs being powered off (sec 5.5.3.2) while in
> > L1.2.
> > 
> > I've been assuming L1.2 exit (which includes Refclk being turned on
> > and PHYs being powered up) is completely handled by hardware, but it
> > sounds like the Qcom controller needs software assistance which fields
> > an interrupt when CLKREQ# is asserted and turns on Refclk and the
> > PHYs?
> > 
> > 5.5.3 does say "All Link and PHY state must be maintained during L1.2,
> > or must be restored upon exit using implementation specific means",
> > and maybe Qcom counts as using implementation specific means.
> > 
> > I *am* concerned about whether software can do the L1.2 exit fast
> > enough, but the biggest reason I'm struggling with this is because
> > using the syscore framework to work around IRQ affinity changes that
> > happen late in suspend just seems kind of kludgy and it doesn't seem
> > like it fits cleanly in the power management model.
> 
> Can you please suggest any another way to work around IRQ affinity
> changes.

One of your earlier patches [1] made dw_msi_mask_irq() look like this:

  static void dw_msi_mask_irq(struct irq_data *d)
  {
    struct pcie_port *pp = irq_data_get_irq_chip_data(d->parent_data);
    struct dw_pcie *pci = to_dw_pcie_from_pp(pp);

    if (dw_pcie_link_up(pci))
	    pci_msi_mask_irq(d);

    irq_chip_mask_parent(d);
  }

That was an awful lot like Marc's suggestion [2] that the
pci_msi_mask_irq() should be redundant.

If it's truly redundant, maybe pci_msi_mask_irq() can be removed
from dw_msi_mask_irq() (and other similar *_mask_irq()
implementations) completely?

Bjorn

[1] https://lore.kernel.org/r/1659526134-22978-3-git-send-email-quic_krichai@quicinc.com
[2] https://lore.kernel.org/linux-pci/86k05m7dkr.wl-maz@kernel.org/