linux-kernel - Re: [PATCH 2/2] PCI: imx6: limit DBI register length

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Date:   Mon, 11 Feb 2019 15:39:00 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     lorenzo.pieralisi@....com, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com, l.stach@...gutronix.de,
        tpiepho@...inj.com, leonard.crestez@....com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] PCI: imx6: limit DBI register length

On Wed, Feb 06, 2019 at 10:57:32AM +0100, Stefan Agner wrote:
> Define the length of the DBI registers. This makes sure that
> the kernel does not access registers beyond that point, avoiding
> the following abort on a i.MX 6Quad:
>   # cat /sys/devices/soc0/soc/1ffc000.pcie/pci0000\:00/0000\:00\:00.0/config
>   [  100.021433] Unhandled fault: imprecise external abort (0x1406) at 0xb6ea7000
>   ...
>   [  100.056423] PC is at dw_pcie_read+0x50/0x84
>   [  100.060790] LR is at dw_pcie_rd_own_conf+0x44/0x48
>   ...

I assume this problem happens when using the pci_read_config() path or
something similar?

Could this be solved using pci_dev.cfg_size instead of building a new
dwc-specific mechanism?  There are some quirks that set dev->cfg_size
to keep from reading past certain points in config space, e.g.,
quirk_citrine(), quirk_nfp6000().

I'm not necessarily opposed to doing it in dwc, but maybe there's some
advantage in reducing the number of ways of doing the same thing.

> Signed-off-by: Stefan Agner <stefan@...er.ch>
> Reviewed-by: Lucas Stach <l.stach@...gutronix.de>
> ---
> Changes in v3:
> - Rebase on pci/dwc
> Changes in v4:
> - Rebase on pci/dwc
> Changes in v5:
> - Rebased ontop of pci/dwc
> - Use DBI length of 0x200
> 
>  drivers/pci/controller/dwc/pci-imx6.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index c1d434ba3642..1ef7be1232f3 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -55,6 +55,7 @@ enum imx6_pcie_variants {
>  struct imx6_pcie_drvdata {
>  	enum imx6_pcie_variants variant;
>  	u32 flags;
> +	int dbi_length;
>  };
>  
>  struct imx6_pcie {
> @@ -1087,6 +1088,8 @@ static int imx6_pcie_probe(struct platform_device *pdev)
>  		break;
>  	}
>  
> +	pci->dbi_length = imx6_pcie->drvdata->dbi_length;
> +
>  	/* Grab turnoff reset */
>  	imx6_pcie->turnoff_reset = devm_reset_control_get_optional_exclusive(dev, "turnoff");
>  	if (IS_ERR(imx6_pcie->turnoff_reset)) {
> @@ -1170,6 +1173,7 @@ static const struct imx6_pcie_drvdata drvdata[] = {
>  		.variant = IMX6Q,
>  		.flags = IMX6_PCIE_FLAG_IMX6_PHY |
>  			 IMX6_PCIE_FLAG_IMX6_SPEED_CHANGE,
> +		.dbi_length = 0x200,
>  	},
>  	[IMX6SX] = {
>  		.variant = IMX6SX,
> -- 
> 2.20.1
>