linux-kernel - [PATCH V2 0/2] nvme: Add support for ACPI StorageD3Enable property

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Date:   Fri, 12 Jun 2020 13:48:18 -0700
From:   "David E. Box" <david.e.box@...ux.intel.com>
To:     shyjumon.n@...el.com, rjw@...ysocki.net, lenb@...nel.org,
        bhelgaas@...gle.com, dan.j.williams@...el.com, kbusch@...nel.org,
        axboe@...com, hch@....de, sagi@...mberg.me
Cc:     "David E. Box" <david.e.box@...ux.intel.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org
Subject: [PATCH V2 0/2] nvme: Add support for ACPI StorageD3Enable property

This patch set implements a solution for a BIOS hack used on some currently
shipping Intel systems to address issues with power management policy
decisions concerning PCIe NVMe drives. Some newer Intel platforms, like
some Comet Lake systems, require that PCIe devices use D3 when doing
suspend-to-idle in order to allow the platform to realize maximum power
savings. This is particularly needed to support ATX power supply shutdown
on desktop systems. In order to ensure this happens for root ports with
storage devices, Microsoft apparently created this ACPI _DSD property as a
way to override their driver policy. To my knowledge this property has not
been discussed with the NVME specification body.

Though the solution is not ideal, it addresses a problem that also affects
Linux since the NVMe driver's default policy of using NVMe APST during
suspend-to-idle would lead to higher power consumption for these platforms.

Patch 1 provides a symbol in the PCI/ACPI layer to read the property.
Patch 2 uses the symbol in the NVMe driver to select D3 as a quirk if set.

Changes from V2:
	- Export the pci_acpi_storage_d3 function for use by drivers as
	  needed instead of modifying the pci header.
	- Add missing put on acpi device handle.
	- Add 'noacpi' module parameter to allow undoing this change.
	- Add info message that this is a platform quirk.

David E. Box (2):
  PCI: Add ACPI StorageD3Enable _DSD support
  drivers/nvme: Add support for ACPI StorageD3Enable property

 drivers/acpi/property.c |  3 +++
 drivers/nvme/host/pci.c | 14 ++++++++++
 drivers/pci/pci-acpi.c  | 59 +++++++++++++++++++++++++++++++++++++++++
 include/linux/pci.h     |  2 ++
 4 files changed, 78 insertions(+)

-- 
2.20.1