ath10k driver crashes whenever firmware crashes on ARM SoC

[Avery Pennarun]

Hi all,

When the ath10k firmware crashes on my device (let's not worry about
why the firmware crashes right now; one problem at a time), my host
CPU (ARMv7 based) can't recover.  I get some variant of this error:

[  780.116977] Unhandled fault: imprecise external abort (0x1406) at 0x2ac3706c
[  780.124336] Internal error: : 1406 [#1] SMP

I've narrowed this down to this code in ath10k/pci.c, ath10k_pci_device_reset:

        /* Put Target, including PCIe, into RESET. */
        val = ath10k_pci_reg_read32(ar, SOC_GLOBAL_RESET_ADDRESS);
        val |= 1;
        ath10k_pci_reg_write32(ar, SOC_GLOBAL_RESET_ADDRESS, val);
        for (i = 0; i < ATH_PCI_RESET_WAIT_MAX; i++) {
                if (ath10k_pci_reg_read32(ar, RTC_STATE_ADDRESS) &
                                          RTC_STATE_COLD_RESET_MASK)
                        break;
                msleep(1);
       }

Specifically, the pci_reg_read32().  I can insert as much time as I
want between the write32 and the read32; it always performs the read,
then crashes with the PC pointing a few instructions later, inside the
msleep(), with the imprecise external abort.  I think this means the
PCI read operation has encountered a PCI target abort, which suggests
that the SOC_GLOBAL_RESET_ADDRESS line has not successfully reset the
device.  From what I understand, on x86 processors PCI target aborts
are not fatal, so you might not notice this problem on those
platforms, but it's bad on ARM.

I'm using the ath10k driver from linux-next 20140117, but I had the
same problem with 3.13-rc2 so I don't think this has changed.

Are other people seeing this?  Is there something I can try to resolve it?

Thanks,

Avery