commit b5a10c5f upstream.

Commit 54adc010 ("nvme/quirk: Add a delay before checking for adapter
readiness") introduced a quirk to adapters that cannot read the bit
NVME_CSTS_RDY right after register NVME_REG_CC is set; these adapters
need a delay or else the action of reading the bit NVME_CSTS_RDY could
somehow corrupt adapter's registers state and it never recovers.

When this quirk was added, we checked ctrl->tagset in order to avoid
quirking in probe time, supposing we would never require such delay
during probe. Well, it was too optimistic; we in fact need this quirk
at probe time in some cases, like after a kexec.

In some experiments, after abnormal shutdown of machine (aka power cord
unplug), we booted into our bootloader in Power, which is a Linux kernel,
and kexec'ed into another distro. If this kexec is too quick, we end up
reaching the probe of NVMe adapter in that distro when adapter is in
bad state (not fully initialized on our bootloader). What happens next
is that nvme_wait_ready() is unable to complete, except if the quirk is
enabled.

So, this patch removes the original ctrl->tagset verification in order
to enable the quirk even on probe time.

Fixes: 54adc010 ("nvme/quirk: Add a delay before checking for adapter readiness")
Reported-by: Andrew Byrne <byrneadw@ie.ibm.com>
Reported-by: Jaime A. H. Gomez <jahgomez@mx1.ibm.com>
Reported-by: Zachary D. Myers <zdmyers@us.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Acked-by: Jeffrey Lien <Jeff.Lien@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[mauricfo: backport to v4.4.70 without nvme quirk handling & nvme_ctrl]
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Tested-by: Narasimhan Vaidyanathan <vnarasimhan@in.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>