cxl: Add mechanism for delivering AFU driver specific events

This adds an afu_driver_ops structure with fetch_event() and
event_delivered() callbacks. An AFU driver such as cxlflash can fill
this out and associate it with a context to enable passing custom AFU
specific events to userspace.

This also adds a new kernel API function cxl_context_pending_events(),
that the AFU driver can use to notify the cxl driver that new specific
events are ready to be delivered, and wake up anyone waiting on the
context wait queue.

The current count of AFU driver specific events is stored in the field
afu_driver_events of the context structure.

The cxl driver checks the afu_driver_events count during poll, select,
read, etc. calls to check if an AFU driver specific event is pending,
and calls fetch_event() to obtain and deliver that event. This way, the
cxl driver takes care of all the usual locking semantics around these
calls and handles all the generic cxl events, so that the AFU driver
only needs to worry about it's own events.

fetch_event() return a struct cxl_event_afu_driver_reserved, allocated
by the AFU driver, and filled in with the specific event information and
size. Total event size (header + data) should not be greater than
CXL_READ_MIN_SIZE (4K).

Th cxl driver prepends an appropriate cxl event header, copies the event
to userspace, and finally calls event_delivered() to return the status of
the operation to the AFU driver. The event is identified by the context
and cxl_event_afu_driver_reserved pointers.

Since AFU drivers provide their own means for userspace to obtain the
AFU file descriptor (i.e. cxlflash uses an ioctl on their scsi file
descriptor to obtain the AFU file descriptor) and the generic cxl driver
will never use this event, the ABI of the event is up to each individual
AFU driver.

Signed-off-by: Philippe Bergheaud <felix@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/uapi/misc/cxl.h b/include/uapi/misc/cxl.h
index 8cd334f99ddc..cbae529b7ce0 100644
--- a/include/uapi/misc/cxl.h
+++ b/include/uapi/misc/cxl.h
@@ -93,6 +93,7 @@ enum cxl_event_type {
 	CXL_EVENT_AFU_INTERRUPT = 1,
 	CXL_EVENT_DATA_STORAGE  = 2,
 	CXL_EVENT_AFU_ERROR     = 3,
+	CXL_EVENT_AFU_DRIVER    = 4,
 };
 
 struct cxl_event_header {
@@ -124,12 +125,28 @@ struct cxl_event_afu_error {
 	__u64 error;
 };
 
+struct cxl_event_afu_driver_reserved {
+	/*
+	 * Defines the buffer passed to the cxl driver by the AFU driver.
+	 *
+	 * This is not ABI since the event header.size passed to the user for
+	 * existing events is set in the read call to sizeof(cxl_event_header)
+	 * + sizeof(whatever event is being dispatched) and the user is already
+	 * required to use a 4K buffer on the read call.
+	 *
+	 * Of course the contents will be ABI, but that's up the AFU driver.
+	 */
+	size_t data_size;
+	u8 data[];
+};
+
 struct cxl_event {
 	struct cxl_event_header header;
 	union {
 		struct cxl_event_afu_interrupt irq;
 		struct cxl_event_data_storage fault;
 		struct cxl_event_afu_error afu_error;
+		struct cxl_event_afu_driver_reserved afu_driver_event;
 	};
 };