Re: [PATCH] PCI: layerscape: use default error response behavior

[Frank Li <Frank.li@oss.nxp.com>]

On Tue, Sep 29, 2026 at 03:43:39PM -0400, jeffbarnes@linux.microsoft.com wrote:
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>
> From: Jeff Barnes <jeffbarnes@linux.microsoft.com>
>
> The Layerscape PCIe driver programs PCIE_ABSERR to forward errors from
> outbound non-posted requests to the internal AXI interface.
>
> A PCI configuration access can race with the link going down after
> dw_pcie_other_conf_map_bus() checks the link but before the MMIO access
> is performed. When the resulting Completion Timeout is forwarded to
> AXI, it causes an asynchronous SError and kernel panic.
>
> For example:
>
>   Kernel panic - not syncing: Asynchronous SError Interrupt
>   ...
>   Call trace:
>    arm64_serror_panic+0x78/0x90
>    do_serror+0x84/0x90
>    el1h_64_error_handler+0x30/0x40
>    el1h_64_error+0x68/0x70
>    pci_generic_config_read+0x64/0xb0
>    dw_pcie_rd_other_conf+0x1c/0x68
>    pci_bus_read_config_word+0x68/0x118
>    pcie_capability_read_word+0xa8/0xd8
>    find_device_iter+0x8c/0x160
>    pci_walk_bus+0x60/0xb8
>    find_source_device+0x78/0xb0
>    aer_isr+0x1dc/0x230
>
> Restore the controller's default error response behavior instead of
> forwarding these errors to AXI.
>
> Reproduce the race by instrumenting dw_pcie_rd_other_conf() to call
> map_bus() while the link is up, then schedule a worker on another CPU
> to set PCI_EXP_LNKCTL_LD. Synchronize the CPUs immediately before the
> Link Disable DBI write, then perform readl() using the address returned
> by map_bus() concurrently with the link transition.
>
> Without this change, the overlapping configuration read results in an
> asynchronous SError and kernel panic. With this change, the same test
> returns 0xffffffff from the configuration read. In this test, AER
> reports a non-fatal Completion Timeout, and no SError or kernel panic
> occurs.
>
> This effectively reverts the error response behavior introduced by
> commit 84d897d69938
> ("PCI: layerscape: Change default error response behavior").

Subject should be revert ...

I am not sure what's expect behavior by other dwc PCI controller. returns
0xfffffffff or report bus error.

Frank

>
> Fixes: 84d897d69938 ("PCI: layerscape: Change default error response behavior")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jeff Barnes <jeffbarnes@linux.microsoft.com>
> ---
>  drivers/pci/controller/dwc/pci-layerscape.c | 12 ------------
>  1 file changed, 12 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pci-layerscape.c b/drivers/pci/controller/dwc/pci-layerscape.c
> index 14d6ac4fc53f..d333f1ae8a41 100644
> --- a/drivers/pci/controller/dwc/pci-layerscape.c
> +++ b/drivers/pci/controller/dwc/pci-layerscape.c
> @@ -28,8 +28,6 @@
>
>  /* PEX Internal Configuration Registers */
>  #define PCIE_STRFMR1           0x71c /* Symbol Timer & Filter Mask Register1 */
> -#define PCIE_ABSERR            0x8d0 /* Bridge Slave Error Response Register */
> -#define PCIE_ABSERR_SETTING    0x9401 /* Forward error of non-posted request */
>
>  /* PF Message Command Register */
>  #define LS_PCIE_PF_MCR         0x2c
> @@ -103,14 +101,6 @@ static void ls_pcie_drop_msg_tlp(struct ls_pcie *pcie)
>         iowrite32(val, pci->dbi_base + PCIE_STRFMR1);
>  }
>
> -/* Forward error response of outbound non-posted requests */
> -static void ls_pcie_fix_error_response(struct ls_pcie *pcie)
> -{
> -       struct dw_pcie *pci = pcie->pci;
> -
> -       iowrite32(PCIE_ABSERR_SETTING, pci->dbi_base + PCIE_ABSERR);
> -}
> -
>  static u32 ls_pcie_pf_lut_readl(struct ls_pcie *pcie, u32 off)
>  {
>         if (pcie->big_endian)
> @@ -180,8 +170,6 @@ static int ls_pcie_host_init(struct dw_pcie_rp *pp)
>         struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>         struct ls_pcie *pcie = to_ls_pcie(pci);
>
> -       ls_pcie_fix_error_response(pcie);
> -
>         dw_pcie_dbi_ro_wr_en(pci);
>         ls_pcie_clear_multifunction(pcie);
>         dw_pcie_dbi_ro_wr_dis(pci);
> --
> 2.43.0
>
>