[PATCH v2] nvme: temporary fix for Apple controller reset

[guenther@tum.de (Stephan Günther)]

Sorry for the addition regarding testing (see below).

On 2015/December/01 09:05, Stephan G?nther wrote:
> On 2015/December/01 12:56, Jens Axboe wrote:
> > On 12/01/2015 12:46 PM, Stephan G?nther wrote:
> > >The patch below has been reviewed by Christoph and reported to work.
> > >However, there is still no sign that it will be applied to linux-4.4.
> > >
> > >Please either undo commit c74dc7801d515d01847fd5cf2b472489fa5717b1,
> > >which added the PCI ID of the Apple controller, or merge the patch below
> > >asap.
> > >
> > >
> > >Currently, the driver will make that controller destroy data!
> > 
> > Honestly, I'd rather revert the pci id addition, unless there's conclusive
> > evidence that limiting the (per queue) depth to 2 really does fix the issue.
> 
> Wes Cilldhaire tested the patch (his answer is in that thread) - as I
> did the past 3 weeks ago as I'm running solely Linux on that broken 
> MacBook.
> 
> > Is this what the OSX driver does? What testing was done to ascertain that 2
> > is the magic number? Does it just make it harder to hit, or does it really
> > fix it?

Any number larger than 2 immediately triggered the problem for me. With 
per-queue depth = 2 it did not happen for 3 weeks.

Moreover, that Apple controller seems to have a single queue...

Best,
Stephan

> 
> I do not know what the OSX driver does. Apple is of absolutely no help
> whatsoever.
> 
> But without that patch `mkfs btrfs` immediately fails. Even `partprobe
> /dev/nvme0n1` will reset the controller (the latter one without data
> loss).
> 
> As I am running a btrfs on a luks container for 3 weeks with that patch,
> it *does* work. Performance is, obviously, not the best one I have seen.
> But given the circumstances I cannot complain at all.
> 
> 
> So again: please either revert the previous patch and leave it to the
> more interested individuals to try it (probably slowing down Linux
> support for that MacBook as not detecting the hard-soldered disk is
> quite a blocker), or merge that hotfix until we find a better solution.
> 
> With 4.5 that may even become a quirk.
> 
> 
> Best,
> Stephan