[PATCH] PCI: imx6: fix downstream bus scanning

[Peter Senna Tschudin]

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.

It solves the issues I was having with latest linux-next when my u-boot
do not initialize PCI. Before this patch system does not boot, after
this patch system boot and the two e1000 devices that are under the PLX
PCI bridge are properly detected. Thank you Lucas!

> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
Tested-by: Peter Senna Tschudin <peter.senna at collabora.com>
> ---
> 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
>