[PATCH] PCI: imx6: fix downstream bus scanning

[Bjorn Helgaas]

On Wed, May 10, 2017 at 07:57:52PM +0200, Lucas Stach wrote:
> The change in Linux 4.12 to make PCI configuartion requests non-posted
> means that we are now getting a synchronous abort when the CFG space
> read to probe for downstream devices times out.
> 
> Synchronous aborts need to be handled differently from the async aborts
> we were getting before, in particular the PC needs to be advanced when
> resolving the abort. This is mostly a copy of what other PCI drivers do
> on ARM to handle those aborts.
> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>

Applied to for-linus for v4.12 with tested-by and acks from Fabio,
Peter, and Richard.  I updated the subject line to:

  PCI: imx6: Fix config read timeout handling

because I don't think this change is specific to bus scanning and I
wanted a hint that it's related to the config space mapping changes.

In fact, I'd really like to include the specific commit that caused
this problem so that if the original commit is backported, there's a
hint that we should backport this one, too.  I *think* it might be
cc7b0d495589, so I updated the changelog to this:

  Commit cc7b0d495589 ("PCI: designware: Update PCI config space remap 
  function") made PCI configuration requests non-posted, which means we now
  get a synchronous abort when the CFG space read to probe for downstream
  devices times out. 

  Synchronous aborts need to be handled differently from the async aborts we
  were getting before, in particular the PC needs to be advanced when
  resolving the abort.  This is mostly a copy of what other PCI drivers do on
  ARM to handle those aborts.

  [bhelgaas: changelog, "Fixes"]
  Fixes: cc7b0d495589 ("PCI: designware: Update PCI config space remap function")

Please let me know if this is the wrong commit.

> ---
> This is a fix that needs to go in for 4.12, but I would hope to get
> some thorough testing before.
> ---
>  drivers/pci/dwc/pci-imx6.c | 33 ++++++++++++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/dwc/pci-imx6.c b/drivers/pci/dwc/pci-imx6.c
> index a98cba55c7f0..19a289b8cc94 100644
> --- a/drivers/pci/dwc/pci-imx6.c
> +++ b/drivers/pci/dwc/pci-imx6.c
> @@ -252,7 +252,34 @@ static void imx6_pcie_reset_phy(struct imx6_pcie *imx6_pcie)
>  static int imx6q_pcie_abort_handler(unsigned long addr,
>  		unsigned int fsr, struct pt_regs *regs)
>  {
> -	return 0;
> +	unsigned long pc = instruction_pointer(regs);
> +	unsigned long instr = *(unsigned long *)pc;
> +	int reg = (instr >> 12) & 15;
> +
> +	/*
> +	 * If the instruction being executed was a read,
> +	 * make it look like it read all-ones.
> +	 */
> +	if ((instr & 0x0c100000) == 0x04100000) {
> +		unsigned long val;
> +
> +		if (instr & 0x00400000)
> +			val = 255;
> +		else
> +			val = -1;
> +
> +		regs->uregs[reg] = val;
> +		regs->ARM_pc += 4;
> +		return 0;
> +	}
> +
> +	if ((instr & 0x0e100090) == 0x00100090) {
> +		regs->uregs[reg] = -1;
> +		regs->ARM_pc += 4;
> +		return 0;
> +	}
> +
> +	return 1;
>  }
>  
>  static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
> @@ -819,8 +846,8 @@ static int __init imx6_pcie_init(void)
>  	 * we can install the handler here without risking it
>  	 * accessing some uninitialized driver state.
>  	 */
> -	hook_fault_code(16 + 6, imx6q_pcie_abort_handler, SIGBUS, 0,
> -			"imprecise external abort");
> +	hook_fault_code(8, imx6q_pcie_abort_handler, SIGBUS, 0,
> +			"external abort on non-linefetch");
>  
>  	return platform_driver_register(&imx6_pcie_driver);
>  }
> -- 
> 2.11.0
> 
> 
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