linux-kernel - Re: [PATCH] PCI: imx6: install the fault handler only if we are really running on a compatible device

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Message-ID: <20230308184922.GA1029723@bhelgaas>
Date:   Wed, 8 Mar 2023 12:49:22 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Richard Zhu <hongxing.zhu@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com
Subject: Re: [PATCH] PCI: imx6: install the fault handler only if we are
 really running on a compatible device

On Tue, Feb 28, 2023 at 09:43:54AM +0100, H. Nikolaus Schaller wrote:
> commit bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
> added a fault hook to this driver in the probe function. So it was only
> installed if needed.
> 
> commit bde4a5a00e76 ("PCI: imx6: Allow probe deferral by reset GPIO")
> moved it from probe to driver init which installs the hook unconditionally
> as soon as the driver is compiled into a kernel.
> 
> When this driver is compiled as a module, the hook is not registered
> until after the driver has been matched with a .compatible and
> loaded.
> 
> commit 415b6185c541 ("PCI: imx6: Fix config read timeout handling")
> extended the fault handling code.
> 
> commit 2d8ed461dbc9 ("PCI: imx6: Add support for i.MX8MQ")
> added some protection for non-ARM architectures, but this does not
> protect non-i.MX ARM architectures.

Are *all* these commits relevant?  Question also applies to Fixes:
below.

> Since fault handlers can be triggered on any architecture for different
> reasons, there is no guarantee that they will be triggered only for the
> assumed situation, leading to improper error handling (i.MX6-specific
> imx6q_pcie_abort_handler) on foreign systems.
> 
> I had seen strange L3 imprecise external abort messages several times on
> OMAP4 and OMAP5 devices and couldn't make sense of them until I realized
> they were related to this unused imx6q driver because I had
> CONFIG_PCI_IMX6=y.

Apparently imx6q_pcie_abort_handler() assumes it is always called
because of a PCI abort?  If so, that sounds problematic.

If non-PCI imprecise aborts happen on OMAP4 and OMAP5 where imx6q is
unused and imx6q_pcie_abort_handler() is not appropriate, I assume
similar non-PCI aborts can also happen on systems where imx6q *is*
used.

So imx6q_pcie_abort_handler() may be trying to fixup non-PCI aborts
when it shouldn't?

> Note that CONFIG_PCI_IMX6=y is useful for kernel binaries that are designed
> to run on different ARM SoC and be differentiated only by device tree
> binaries. So turning off CONFIG_PCI_IMX6 is not a solution.
> 
> Therefore we check the compatible in the init function before registering
> the fault handler.
> 
> Fixes: bde4a5a00e76 ("PCI: imx6: Allow probe deferral by reset GPIO")
> Fixes: 415b6185c541 ("PCI: imx6: Fix config read timeout handling")
> Fixes: 2d8ed461dbc9 ("PCI: imx6: Add support for i.MX8MQ")
> 
> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 1dde5c579edc8..89774aa187ae8 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1402,6 +1402,15 @@ DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_SYNOPSYS, 0xabcd,
>  static int __init imx6_pcie_init(void)
>  {
>  #ifdef CONFIG_ARM
> +	const struct of_device_id *reboot_id;
> +	struct device_node *np;
> +
> +	np = of_find_matching_node_and_match(NULL, imx6_pcie_of_match,
> +					     &reboot_id);

Since you don't need reboot_id, I think you should use
of_find_matching_node() instead.

> +	if (!np)
> +		return -ENODEV;
> +	of_node_put(np);
> +
>  	/*
>  	 * Since probe() can be deferred we need to make sure that
>  	 * hook_fault_code is not called after __init memory is freed
> -- 
> 2.38.1
>