NVME controller issue prevents boot on Kernel versions >= 5.8 on MacBook 7,1 (MacBook Air 2015)

[Keith Busch]

On Thu, Oct 29, 2020 at 09:31:12PM -0700, B.L. Jones wrote:
> Hello all,
> 
> This is my first time emailing any kernel mail list so I will do my
> best to furnish any information you may need regarding this.
> 
> To begin, I reported a boot issue against the kernel on the
> Fedora/RedHat Bugzilla last month here:
> https://bugzilla.redhat.com/show_bug.cgi?id=1878596
> 
> Essentially, booting any kernel greater than version 5.8 on my 2015
> MacBook Air would cause a soft freeze, with an error stating:
> 
> [   34.890739] f-air kernel: nvme nvme0: controller is down; will reset: CSTS=0x3, PCI_STATUS=0x10
> [   34.917820] f-air kernel: nvme nvme0: detected Apple NVMe controller, set queue depth=2 to work around controller resets
> 
> Another individual in the bugzilla thread took a look at the error
> logs and identified a potential commit that may have caused the issue:
> 
> commit 54b2fcee1db041a83b52b51752dade6090cf952f
> Author: Keith Busch <kbusch at kernel.org>
> Date:   Mon Apr 27 11:54:46 2020 -0700
> 
>     nvme-pci: remove last_sq_tail
> 
>     The nvme driver does not have enough tags to wrap the queue, and blk-mq
>     will no longer call commit_rqs() when there are no new submissions to
>     notify.
> 
>     Signed-off-by: Keith Busch <kbusch at kernel.org>

Thanks for the notice. I'll see if I can fix this, but I think a revert
may be necessary.