Intel SATA AHCI controllers support a strange mode where NVMe devices disappear from the PCI bus, and instead are remapped into AHCI PCI memory space. 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. https://marc.info/?l=linux-ide&m=147709610621480&w=2 Since then: - Intel stopped developing these patches & hasn't been responding to my emails on this topic. - More register documentation appeared in https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/300-series-chipset-pch-datasheet-vol-2.pdf - 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. https://marc.info/?l=linux-pci&m=156034736822205&w=2 - 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 challenge. - 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 -- 2.20.1
