Re: [PATCH] ahci: Add support for EEH error recovery

[Brian King <brking@linux.vnet.ibm.com>]

On 05/14/2015 10:48 AM, Tejun Heo wrote:
> Hello, Brian.
> 
> On Thu, May 14, 2015 at 10:44:18AM -0500, Brian King wrote:
>> So, on the Power platform, the pci_error_handlers map to our EEH recovery.
> 
> What's EEH?

It stands for "Extended Error Handling". 

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/PCI/pci-error-recovery.txt
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/powerpc/eeh-pci-error-recovery.txt

> 
>> In that case, without this patch, if we hit any sort of PCIe error, we
>> won't be able to recover and we'll lose all access to the ahci disks.
>> This could be the adapter trying to access an invalid DMA address due
>> to a transient hardware issue, or it could be due to a driver bug giving
>> the adapter an invalid address. It could also be other various PCIe
>> errors that cause our PCIe bridge chip to isolate the device and
>> place it into the EEH "frozen" state. When this occurs, if the driver
>> associated with the hardware does not have these handlers registered,
>> powerpc arch kernel code will hotplug remove the adapter, recover the
>> adapter, then hotplug add it back. This works OK for some devices,
>> but generally not so well for storage devices with mounted filesystems,
>> which would tend to go readonly in this case.
> 
> I think the above, with more details on how the error handling
> actually works (IOW what it does), should be in the patch description
> and comments.  Wen, can you please update the patch with more
> information?

Agreed.

Thanks,

Brian

-- 
Brian King
Power Linux I/O
IBM Linux Technology Center