[PATCH V14 0/7] CXL: Read CDAT

From: ira . weiny
Date: Thu Jul 14 2022 - 23:04:38 EST

From: Ira Weiny <ira.weiny@xxxxxxxxx>

Details of changes are in the individual patches.

Major changes from V13:[10]
Dan minor updates
Willy's suggestion of documentation is good but I'm deferring it until
we get the location of the PCI mailboxes settled.
Drop retry CDAT patch
Drop DSMAS patch
Rebased on latest cxl-pending

CXL drivers need various data which are provided through generic DOE mailboxes
as defined in the PCIe 6.0 spec.[1]

One such data is the Coherent Device Attribute Table (CDAT). CDAT data provides
coherent information about the various devices in the system. It was developed
because systems no longer have a priori knowledge of all coherent devices
within a system. CDAT describes the coherent characteristics of the
components on the CXL bus separate from system configurations. The OS can
then, for example, use this information to form correct interleave sets.

To begin reading the CDAT the OS must have support to access the DOE mailboxes
provided by the CXL devices.

Because DOE is not specific to DOE but is provided within the PCI spec, the
series adds PCI DOE capability library functions. These functions allow for
the iteration of the DOE capabilities on a device as well as creating
pci_doe_mb structures which can control the operation of the DOE state machine.

For now the iteration of and storage of the DOE mailboxes is done on memdev
objects within the CXL stack. When this is needed in more generic code this
can be lifted later.

This work was tested using qemu.

[0] https://lore.kernel.org/linux-cxl/20211105235056.3711389-1-ira.weiny@xxxxxxxxx/
[1] https://pcisig.com/specifications
[2] https://lore.kernel.org/qemu-devel/20210202005948.241655-1-ben.widawsky@xxxxxxxxx/
[3] https://lore.kernel.org/linux-cxl/20220201071952.900068-1-ira.weiny@xxxxxxxxx/
[4] https://lore.kernel.org/linux-cxl/20220330235920.2800929-1-ira.weiny@xxxxxxxxx/
[5] https://lore.kernel.org/linux-cxl/20220414203237.2198665-1-ira.weiny@xxxxxxxxx/
[6] https://lore.kernel.org/linux-cxl/20220531152632.1397976-1-ira.weiny@xxxxxxxxx/
[7] https://lore.kernel.org/linux-cxl/20220605005049.2155874-1-ira.weiny@xxxxxxxxx/
[8] https://lore.kernel.org/linux-cxl/20220610202259.3544623-1-ira.weiny@xxxxxxxxx/
[9] https://lore.kernel.org/linux-cxl/20220628041527.742333-1-ira.weiny@xxxxxxxxx/
[10] https://lore.kernel.org/linux-cxl/20220705154932.2141021-1-ira.weiny@xxxxxxxxx/

Previous changes

Changes from V12:[9]
A couple of bug fixes in the new XArray stuff
Remove the IRQ support because I did not realize how that worked and it
was complicating things.
Remove busy retries and replace with an error as there is no good way
to ensure it will work.
Other code clean ups mentioned in the individual patches.

Changes from V11:[8]
The major change in this version is to remove the workqueue from the
internal implementation of the state machine. A single ordered
workqueue within each mailbox processes tasks submitted. This
workqueue takes care of all locking and guarantees that tasks are
completed in the order submitted. Any synchronization which is
required between tasks will need to be handled by the user of the
mailbox. However, the user can depend on work items being completed in
the order they are submitted. So a single thread submitter is
guaranteed to get all work items completed in order. This also aids in
the support of a single mailbox supporting multiple protocols. Each
protocol could have a separate thread submitting tasks for that
protocol. The mailbox object will ensure that each protocol task is
complete before another task starts. But multiple user threads can be
submitting tasks for different protocols all at the same time without
regard to other protocols being used.

XArrays are used throughout the series.

Other minor changes are noted in the individual patches.

Changes from V10:[7]
Address Ben Widawsky's comments
Protect against potentially malicious devices.
Fix ownership issue of cdat_mb

Changes from V9:[6]
Address feedback from
Lukas Wunner, Davidlohr Bueso, Jonathan Cameron,
Alison Schofield, and Ben Widawsky
Details in each individual patch.

Changes from V8:[5]
For this version I've punted a bit to get it out and drop the auxiliary
bus functionality. I like where Jonathan is going with the port driver
idea. I think eventually the irq/mailbox creation will need to be more
generic in a PCI port driver. I've modeled this version on such an
architecture but used the CXL port for the time being.

From Dan
Drop the auxiliary bus/device
From Jonathan
From Bjorn
Clean up commit messages
move pci-doe.c to doe.c
Clean up PCI spec references
Ensure all messages use pci_*()
Add offset to error messages to distinguish mailboxes
use hex for DOE offsets
Print 4 nibbles for Vendor ID and 2 for type.
s/irq/IRQ in comments
Fix long lines
Fix typos

Changes from V7:[4]
Avoid code bloat by making pci-doe.c conditional on CONFIG_PCI_DOE
which is auto selected by the CXL_PCI config option.
Minor code clean ups
Fix bug in pci_doe_supports_prot()
Rebase to cxl-pending

Changes from V6:[3]
The big change is the removal of the auxiliary bus code from the PCI
layer. The auxiliary bus usage is now in the CXL layer. The PCI layer
provides helpers for subsystems to utilize DOE mailboxes by creating a
pci_doe_mb object which controls a state machine for that mailbox
capability. The CXL layer wraps this object in an auxiliary device and
driver which can then be used to determine if the kernel is controlling
the capability or it is available to be used by user space. Reads from
user space via lspci are allowed. Writes are allowed but flagged via a
tainting the kernel.

Feedback from Bjorn, Jonathan, and Dan
Details in each patch

Changes from V5:[0]

Rework the patch set to split PCI vs CXL changes
Also make each change a bit more stand alone for easier review
Add cxl_cdat structure
Put CDAT related data structures in cdat.h
Clarify some device lifetimes with comments
Incorporate feedback from Jonathan, Bjorn and Dan
The bigest change is placing the DOE scanning code into the
pci_doe driver (part of the PCI codre).
Validate the CDAT when it is read rather than before DSMAS
Do not report DSMAS failure as an error, report a warning and
keep going.
Retry reading the table 1 time.
Update commit messages and this cover letter

Ira Weiny (5):
PCI: Replace magic constant for PCI Sig Vendor ID
cxl/pci: Create PCI DOE mailbox's for memory devices
driver-core: Introduce BIN_ATTR_ADMIN_{RO,RW}
cxl/port: Read CDAT table
cxl/port: Introduce cxl_cdat_valid()

Jonathan Cameron (2):
PCI: Add vendor ID for the PCI SIG
PCI/DOE: Add DOE mailbox support functions

.clang-format | 1 +
Documentation/ABI/testing/sysfs-bus-cxl | 10 +
drivers/cxl/Kconfig | 1 +
drivers/cxl/cdat.h | 63 +++
drivers/cxl/core/pci.c | 206 +++++++++
drivers/cxl/cxl.h | 5 +
drivers/cxl/cxlmem.h | 3 +
drivers/cxl/cxlpci.h | 1 +
drivers/cxl/pci.c | 44 ++
drivers/cxl/port.c | 54 +++
drivers/pci/Kconfig | 3 +
drivers/pci/Makefile | 1 +
drivers/pci/doe.c | 546 ++++++++++++++++++++++++
drivers/pci/probe.c | 2 +-
include/linux/pci-doe.h | 79 ++++
include/linux/pci_ids.h | 1 +
include/linux/sysfs.h | 16 +
include/uapi/linux/pci_regs.h | 29 +-
18 files changed, 1063 insertions(+), 2 deletions(-)
create mode 100644 drivers/cxl/cdat.h
create mode 100644 drivers/pci/doe.c
create mode 100644 include/linux/pci-doe.h

base-commit: b060edfd8cdd52bc8648392500bf152a8dd6d4c5