linux-kernel - Re: [PATCH RESEND] PCI: dwc: Fix MSI not work after resume

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Message-ID: <20210323012441.GA515937@bjorn-Precision-5520>
Date:   Mon, 22 Mar 2021 20:24:41 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kishon Vijay Abraham I <kishon@...com>,
        Richard Zhu <hongxing.zhu@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Dilip Kota <eswara.kota@...ux.intel.com>
Subject: Re: [PATCH RESEND] PCI: dwc: Fix MSI not work after resume

[+cc Kishon, Richard, Lucas, Dilip]

On Mon, Mar 01, 2021 at 11:10:31AM +0800, Jisheng Zhang wrote:
> After we move dw_pcie_msi_init() into core -- dw_pcie_host_init(), the
> MSI stops working after resume. Because dw_pcie_host_init() is only
> called once during probe. To fix this issue, we move dw_pcie_msi_init()
> to dw_pcie_setup_rc().

This patch looks fine, but I don't think the commit log tells the
whole story.

Prior to 59fbab1ae40e, it looks like the only dwc-based drivers with
resume functions were dra7xx, imx6, intel-gw, and tegra [1].

Only tegra called dw_pcie_msi_init() in the resume path, and I do
think 59fbab1ae40e broke MSI after resume because it removed the
dw_pcie_msi_init() call from tegra_pcie_enable_msi_interrupts().

I'm not convinced this patch fixes it reliably, though.  The call
chain looks like this:

  tegra_pcie_dw_resume_noirq
    tegra_pcie_dw_start_link
      if (dw_pcie_wait_for_link(pci))
        dw_pcie_setup_rc

dw_pcie_wait_for_link() returns 0 if the link is up, so we only call
dw_pcie_setup_rc() in the case where the link *didn't* come up.  If
the link comes up nicely without retry, we won't call
dw_pcie_setup_rc() and hence won't call dw_pcie_msi_init().

Since then, exynos added a resume function.  My guess is MSI never
worked after resume for dra7xx, exynos, imx6, and intel-gw because
they don't call dw_pcie_msi_init() in their resume functions.

This patch looks like it should fix MSI after resume for exynos, imx6,
and intel-gw because they *do* call dw_pcie_setup_rc() from their
resume functions [2], and after this patch, dw_pcie_msi_init() will be
called from there.

I suspect MSI after resume still doesn't work on dra7xx.

[1] git grep -A20 -e "static.*resume_noirq" 59fbab1ae40e^:drivers/pci/controller/dwc
[2] git grep -A20 -e "static.*resume_noirq" drivers/pci/controller/dwc

> Fixes: 59fbab1ae40e ("PCI: dwc: Move dw_pcie_msi_init() into core")
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> ---
> Since v1:
>  - collect Reviewed-by tag
> 
>  drivers/pci/controller/dwc/pcie-designware-host.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 7e55b2b66182..e6c274f4485c 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -400,7 +400,6 @@ int dw_pcie_host_init(struct pcie_port *pp)
>  	}
>  
>  	dw_pcie_setup_rc(pp);
> -	dw_pcie_msi_init(pp);
>  
>  	if (!dw_pcie_link_up(pci) && pci->ops && pci->ops->start_link) {
>  		ret = pci->ops->start_link(pci);
> @@ -551,6 +550,8 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
>  		}
>  	}
>  
> +	dw_pcie_msi_init(pp);
> +
>  	/* Setup RC BARs */
>  	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_0, 0x00000004);
>  	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_1, 0x00000000);
> -- 
> 2.30.1
>