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Unlike the cxl_pci class driver that opportunistically enables memory expansion with no other dependent functionality, CXL accelerator drivers have distinct PCIe-only and CXL-enhanced operation states. If CXL is available some additional coherent memory/cache operations can be enabled, otherwise traditional DMA+MMIO over PCIe/CXL.io is a fallback. This constitutes a new mode of operation where the caller of devm_cxl_add_memdev() wants to make a "go/no-go" decision about running in CXL accelerated mode or falling back to PCIe-only operation. Part of that decision making process likely also includes additional CXL-acceleration-specific resource setup. Encapsulate both of those requirements into 'struct cxl_memdev_attach' that provides a ->probe() callback. The probe callback runs in cxl_mem_probe() context, after the port topology is successfully attached for the given memdev. It supports a contract where, upon successful return from devm_cxl_add_memdev(), everything needed for CXL accelerated operation has been enabled. Additionally the presence of @cxlmd->attach indicates that the accelerator driver be detached when CXL operation ends. This conceptually makes a CXL link loss event mirror a PCIe link loss event which results in triggering the ->remove() callback of affected devices+drivers. A driver can re-attach to recover back to PCIe-only operation. Live recovery, i.e. without a ->remove()/->probe() cycle, is left as a future consideration. [ dj: Repalce with updated commit log from Dan ] Cc: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com> Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com> Reviewed-by: Dave Jiang <dave.jiang@intel.com> Tested-by: Alejandro Lucero <alucerop@amd.com> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com> Link: https://patch.msgid.link/20251216005616.3090129-7-dan.j.williams@intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Dave Jiang <dave.jiang@intel.com>