Explain the binding process for sysram and daxdev regions which are explicit about which dax driver to use during region creation.
Jonathan Corbet <[email protected]> Signed-off-by: Gregory Price <[email protected]> --- .../driver-api/cxl/linux/cxl-driver.rst | 43 +++++++++++++++++++ .../driver-api/cxl/linux/dax-driver.rst | 29 +++++++++++++ 2 files changed, 72 insertions(+) diff --git a/Documentation/driver-api/cxl/linux/cxl-driver.rst b/Documentation/driver-api/cxl/linux/cxl-driver.rst index dd6dd17dc536..1f857345e896 100644 --- a/Documentation/driver-api/cxl/linux/cxl-driver.rst +++ b/Documentation/driver-api/cxl/linux/cxl-driver.rst @@ -445,6 +445,49 @@ for more details. :: dax0.0 devtype modalias uevent dax_region driver subsystem +DAX regions are created when a CXL RAM region is bound to one of the +following drivers: + +* :code:`cxl_devdax_region` - Creates a dax_region for device_dax mode. + The resulting DAX device provides direct userspace access via + :code:`/dev/daxN.Y`. + +* :code:`cxl_dax_kmem_region` - Creates a dax_region for kmem mode via a + sysram_region intermediate device. See `Sysram Region`_ below. + +Sysram Region +~~~~~~~~~~~~~ +A `Sysram Region` is an intermediate device between a CXL `Memory Region` +and a `DAX Region` for kmem mode. It is created when a CXL RAM region is +bound to the :code:`cxl_sysram_region` driver. + +The sysram_region device provides an interposition point where users can +configure memory hotplug policy before the underlying dax_region is created +and memory is hotplugged to the system. + +The device hierarchy for kmem mode is:: + + regionX -> sysram_regionX -> dax_regionX -> daxX.Y + +The sysram_region exposes an :code:`online_type` attribute that controls +how memory will be onlined when the dax_kmem driver binds: + +* :code:`invalid` - Not configured (default). Blocks driver binding. +* :code:`offline` - Memory will not be onlined automatically. +* :code:`online` - Memory will be onlined in ZONE_NORMAL. +* :code:`online_movable` - Memory will be onlined in ZONE_MOVABLE. + +Example two-stage binding process:: + + # Bind region to sysram_region driver + echo region0 > /sys/bus/cxl/drivers/cxl_sysram_region/bind + + # Configure memory online type + echo online_movable > /sys/bus/cxl/devices/sysram_region0/online_type + + # Bind sysram_region to dax_kmem_region driver + echo sysram_region0 > /sys/bus/cxl/drivers/cxl_dax_kmem_region/bind + Mailbox Interfaces ------------------ A mailbox command interface for each device is exposed in :: diff --git a/Documentation/driver-api/cxl/linux/dax-driver.rst b/Documentation/driver-api/cxl/linux/dax-driver.rst index 10d953a2167b..2b8e21736292 100644 --- a/Documentation/driver-api/cxl/linux/dax-driver.rst +++ b/Documentation/driver-api/cxl/linux/dax-driver.rst @@ -17,6 +17,35 @@ The DAX subsystem exposes this ability through the `cxl_dax_region` driver. A `dax_region` provides the translation between a CXL `memory_region` and a `DAX Device`. +CXL DAX Region Drivers +====================== +CXL provides multiple drivers for creating DAX regions, each suited for +different use cases: + +cxl_devdax_region +----------------- +The :code:`cxl_devdax_region` driver creates a dax_region configured for +device_dax mode. When a CXL RAM region is bound to this driver, the +resulting DAX device provides direct userspace access via :code:`/dev/daxN.Y`. + +Device hierarchy:: + + regionX -> dax_regionX -> daxX.Y + +This is the simplest path for applications that want to manage CXL memory +directly from userspace. + +cxl_dax_kmem_region +------------------- +For kmem mode, CXL provides a two-stage binding process that allows users +to configure memory hotplug policy before memory is added to the system. + +The :code:`cxl_dax_kmem_region` driver then binds a sysram_region +device and creates a dax_region configured for kmem mode. + +The :code:`online_type` policy will be passed from sysram_region to +the dax kmem driver for use when hotplugging the memory. + DAX Device ========== A `DAX Device` is a file-like interface exposed in :code:`/dev/daxN.Y`. A -- 2.52.0
