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, 56 insertions, 8 deletions

diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index eec468f1612f..5fb9894b157f 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -293,6 +293,17 @@ int afu_mmap(struct file *file, struct vm_area_struct *vm)
 	return cxl_context_iomap(ctx, vm);
 }
 
+static inline bool ctx_event_pending(struct cxl_context *ctx)
+{
+	if (ctx->pending_irq || ctx->pending_fault || ctx->pending_afu_err)
+		return true;
+
+	if (ctx->afu_driver_ops && atomic_read(&ctx->afu_driver_events))
+		return true;
+
+	return false;
+}
+
 unsigned int afu_poll(struct file *file, struct poll_table_struct *poll)
 {
 	struct cxl_context *ctx = file->private_data;
@@ -305,8 +316,7 @@ unsigned int afu_poll(struct file *file, struct poll_table_struct *poll)
 	pr_devel("afu_poll wait done pe: %i\n", ctx->pe);
 
 	spin_lock_irqsave(&ctx->lock, flags);
-	if (ctx->pending_irq || ctx->pending_fault ||
-	    ctx->pending_afu_err)
+	if (ctx_event_pending(ctx))
 		mask |= POLLIN | POLLRDNORM;
 	else if (ctx->status == CLOSED)
 		/* Only error on closed when there are no futher events pending
@@ -319,16 +329,46 @@ unsigned int afu_poll(struct file *file, struct poll_table_struct *poll)
 	return mask;
 }
 
-static inline int ctx_event_pending(struct cxl_context *ctx)
+static ssize_t afu_driver_event_copy(struct cxl_context *ctx,
+				     char __user *buf,
+				     struct cxl_event *event,
+				     struct cxl_event_afu_driver_reserved *pl)
 {
-	return (ctx->pending_irq || ctx->pending_fault ||
-	    ctx->pending_afu_err || (ctx->status == CLOSED));
+	/* Check event */
+	if (!pl) {
+		ctx->afu_driver_ops->event_delivered(ctx, pl, -EINVAL);
+		return -EFAULT;
+	}
+
+	/* Check event size */
+	event->header.size += pl->data_size;
+	if (event->header.size > CXL_READ_MIN_SIZE) {
+		ctx->afu_driver_ops->event_delivered(ctx, pl, -EINVAL);
+		return -EFAULT;
+	}
+
+	/* Copy event header */
+	if (copy_to_user(buf, event, sizeof(struct cxl_event_header))) {
+		ctx->afu_driver_ops->event_delivered(ctx, pl, -EFAULT);
+		return -EFAULT;
+	}
+
+	/* Copy event data */
+	buf += sizeof(struct cxl_event_header);
+	if (copy_to_user(buf, &pl->data, pl->data_size)) {
+		ctx->afu_driver_ops->event_delivered(ctx, pl, -EFAULT);
+		return -EFAULT;
+	}
+
+	ctx->afu_driver_ops->event_delivered(ctx, pl, 0); /* Success */
+	return event->header.size;
 }
 
 ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 			loff_t *off)
 {
 	struct cxl_context *ctx = file->private_data;
+	struct cxl_event_afu_driver_reserved *pl = NULL;
 	struct cxl_event event;
 	unsigned long flags;
 	int rc;
@@ -344,7 +384,7 @@ ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 
 	for (;;) {
 		prepare_to_wait(&ctx->wq, &wait, TASK_INTERRUPTIBLE);
-		if (ctx_event_pending(ctx))
+		if (ctx_event_pending(ctx) || (ctx->status == CLOSED))
 			break;
 
 		if (!cxl_ops->link_ok(ctx->afu->adapter, ctx->afu)) {
@@ -374,7 +414,12 @@ ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 	memset(&event, 0, sizeof(event));
 	event.header.process_element = ctx->pe;
 	event.header.size = sizeof(struct cxl_event_header);
-	if (ctx->pending_irq) {
+	if (ctx->afu_driver_ops && atomic_read(&ctx->afu_driver_events)) {
+		pr_devel("afu_read delivering AFU driver specific event\n");
+		pl = ctx->afu_driver_ops->fetch_event(ctx);
+		atomic_dec(&ctx->afu_driver_events);
+		event.header.type = CXL_EVENT_AFU_DRIVER;
+	} else if (ctx->pending_irq) {
 		pr_devel("afu_read delivering AFU interrupt\n");
 		event.header.size += sizeof(struct cxl_event_afu_interrupt);
 		event.header.type = CXL_EVENT_AFU_INTERRUPT;
@@ -404,6 +449,9 @@ ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 
 	spin_unlock_irqrestore(&ctx->lock, flags);
 
+	if (event.header.type == CXL_EVENT_AFU_DRIVER)
+		return afu_driver_event_copy(ctx, buf, &event, pl);
+
 	if (copy_to_user(buf, &event, event.header.size))
 		return -EFAULT;
 	return event.header.size;
@@ -558,7 +606,7 @@ int __init cxl_file_init(void)
 	 * If these change we really need to update API.  Either change some
 	 * flags or update API version number CXL_API_VERSION.
 	 */
-	BUILD_BUG_ON(CXL_API_VERSION != 2);
+	BUILD_BUG_ON(CXL_API_VERSION != 3);
 	BUILD_BUG_ON(sizeof(struct cxl_ioctl_start_work) != 64);
 	BUILD_BUG_ON(sizeof(struct cxl_event_header) != 8);
 	BUILD_BUG_ON(sizeof(struct cxl_event_afu_interrupt) != 8);