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ARCH_HAS_CPU_CACHE_INVALIDATE_MEMREGION provides the mechanism for
invalidating certain memory regions in a cache-incoherent manner. Currently
this is used by NVDIMM and CXL memory drivers in cases where it is
necessary to flush all data from caches by physical address range.
The operations in question are effectively memory hotplug, where stale
data might otherwise remain in the caches.
This is separate from the invalidates done to enable use of non-coherent
DMA masters, primarily in terms of when it is needed (not related to DMA
mappings) and how deep the flush must push data. The flushes done for
non-coherent DMA only need to reach the Point of Coherence of a single host
(which is often nearer CPUs and DMA masters than the physical storage).
This operation must push the data out of non architectural caches
(memory-side caches, write buffers etc) and typically all the way to the
memory device.
In some architectures these operations are supported by system components
that may become available only later in boot as they are either present
on a discoverable bus, or via a firmware description of an MMIO interface
(e.g. ACPI DSDT). Provide a framework to handle this case.
Architectures can opt in for this support via
CONFIG_GENERIC_CPU_CACHE_MAINTENANCE
Add a registration framework. Each driver provides an ops structure and
the first op is Write Back and Invalidate by PA Range. The driver may
over invalidate.
For systems that can perform this operation asynchronously an optional
completion check operation is also provided. If present that must be called
to ensure that the action has finished. This provides a considerable
performance advantage if multiple agents are involved in the maintenance
operation.
When multiple agents are present in the system each should register with
this framework and the core code will issue the invalidate to all of them
before checking for completion on each. This is done to avoid need for
filtering in the core code which can become complex when interleave,
potentially across different cache coherency hardware is going on, so it
is easier to tell everyone and let those who don't care do nothing.
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
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