[PATCH v2 0/5] Support Intel AHCI remapped NVMe devices

From: Daniel Drake
Date: Thu Jun 20 2019 - 01:18:59 EST

Intel SATA AHCI controllers support a strange mode where NVMe devices
disappear from the PCI bus, and instead are remapped into AHCI PCI memory

Many current and upcoming consumer products ship with the AHCI controller
in this "RAID" or "Intel RST Premium with Intel Optane System Acceleration"
mode by default. Without Linux support for this remapped mode,
the default out-of-the-box experience is that the NVMe storage device
is inaccessible (which in many cases is the only internal storage device).

In most cases, the SATA configuration can be changed in the BIOS menu to
"AHCI", resulting in the AHCI & NVMe devices appearing as separate
devices as you would ordinarily expect. Changing this configuration
is the recommendation for power users because there are several limitations
of the remapped mode (now documented in Kconfig help text).

However, it's also important to support the remapped mode given that
it is an increasingly common product default. We cannot expect ordinary
users of consumer PCs to find out about this situation and then
confidently go into the BIOS menu to change options.

This patch set implements support for the remapped mode.

v1 of these patches was originally posted by Dan Williams in 2016.
Since then:

- Intel stopped developing these patches & hasn't been responding to
my emails on this topic.

- More register documentation appeared in

- I tried Christoph's suggestion of exposing the devices on a fake PCI bus,
hence not requiring NVMe driver changes, but Bjorn Helgaas does not think
it's the right approach and instead recommends the approach taken here.

- More consumer devices have appeared with this setting as the default,
and with the decreasing cost of NVMe storage, it appears that a whole
bunch more consumer PC products currently in development are going to
ship in RAID/remapped mode, with only a single NVMe disk, which Linux
will otherwise be unable to access by default.

- We heard from hardware vendors that this Linux incompatibility is
causing them to consider discontinuing Linux support on affected
products. Changing the BIOS setting is too much of a logistics

- I updated Dan's patches for current kernels. I added docs and references
and incorporated the new register info. I incorporated feedback to push
the recommendation that the user goes back to AHCI mode via the BIOS
setting (in kernel logs and Kconfig help). And made some misc minor
changes that I think are sensible.

- I investigated MSI-X support. Can't quite get it working, but I'm hopeful
that we can figure it out and add it later. With these patches shared
I'll follow up with more details about that. With the focus on
compatibility with default configuration of common consumer products,
I'm hoping we could land an initial version without MSI support before
tending to those complications.

Dan Williams (2):
nvme: rename "pci" operations to "mmio"
nvme: move common definitions to pci.h

Daniel Drake (3):
ahci: Discover Intel remapped NVMe devices
nvme: introduce nvme_dev_ops
nvme: Intel AHCI remap support

drivers/ata/Kconfig | 33 ++
drivers/ata/ahci.c | 173 ++++++++--
drivers/ata/ahci.h | 14 +
drivers/nvme/host/Kconfig | 3 +
drivers/nvme/host/Makefile | 3 +
drivers/nvme/host/intel-ahci-remap.c | 185 ++++++++++
drivers/nvme/host/pci.c | 490 ++++++++++++++-------------
drivers/nvme/host/pci.h | 145 ++++++++
include/linux/ahci-remap.h | 140 +++++++-
9 files changed, 922 insertions(+), 264 deletions(-)
create mode 100644 drivers/nvme/host/intel-ahci-remap.c
create mode 100644 drivers/nvme/host/pci.h