RDMA/siw: Change CQ flags from 64->32 bits

This patch changes the driver/user shared (mmapped) CQ notification
flags field from unsigned 64-bits size to unsigned 32-bits size. This
enables building siw on 32-bit architectures.

This patch changes the siw-abi, but as siw was only just merged in
this merge window cycle, there are no released kernels with the prior
abi. We are making no attempt to be binary compatible with siw user
space libraries prior to the merge of siw into the upstream kernel,
only moving forward with upstream kernels and upstream rdma-core
provided siw libraries are we guaranteeing compatibility.

Signed-off-by: Bernard Metzler <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Doug Ledford <[e-mail]>

drivers/infiniband/sw/siw/Kconfig

···
 config RDMA_SIW
 	tristate "Software RDMA over TCP/IP (iWARP) driver"
-	depends on INET && INFINIBAND && LIBCRC32C && 64BIT
+	depends on INET && INFINIBAND && LIBCRC32C
 	select DMA_VIRT_OPS
 	help
 	This driver implements the iWARP RDMA transport over

drivers/infiniband/sw/siw/siw.h

···
 struct siw_cq {
 	struct ib_cq base_cq;
 	spinlock_t lock;
-	u64 *notify;
+	struct siw_cq_ctrl *notify;
 	struct siw_cqe *queue;
 	u32 cq_put;
 	u32 cq_get;

drivers/infiniband/sw/siw/siw_qp.c

···
  */
 static bool siw_cq_notify_now(struct siw_cq *cq, u32 flags)
 {
-	u64 cq_notify;
+	u32 cq_notify;
 
 	if (!cq->base_cq.comp_handler)
 		return false;
 
-	cq_notify = READ_ONCE(*cq->notify);
+	/* Read application shared notification state */
+	cq_notify = READ_ONCE(cq->notify->flags);
 
 	if ((cq_notify & SIW_NOTIFY_NEXT_COMPLETION) ||
 	    ((cq_notify & SIW_NOTIFY_SOLICITED) &&
 	     (flags & SIW_WQE_SOLICITED))) {
-		/* dis-arm CQ */
-		smp_store_mb(*cq->notify, SIW_NOTIFY_NOT);
+		/*
+		 * CQ notification is one-shot: Since the
+		 * current CQE causes user notification,
+		 * the CQ gets dis-aremd and must be re-aremd
+		 * by the user for a new notification.
+		 */
+		WRITE_ONCE(cq->notify->flags, SIW_NOTIFY_NOT);
 
 		return true;
 	}

drivers/infiniband/sw/siw/siw_verbs.c

···
 
 	spin_lock_init(&cq->lock);
 
-	cq->notify = &((struct siw_cq_ctrl *)&cq->queue[size])->notify;
+	cq->notify = (struct siw_cq_ctrl *)&cq->queue[size];
 
 	if (udata) {
 		struct siw_uresp_create_cq uresp = {};
···
 	siw_dbg_cq(cq, "flags: 0x%02x\n", flags);
 
 	if ((flags & IB_CQ_SOLICITED_MASK) == IB_CQ_SOLICITED)
-		/* CQ event for next solicited completion */
-		smp_store_mb(*cq->notify, SIW_NOTIFY_SOLICITED);
+		/*
+		 * Enable CQ event for next solicited completion.
+		 * and make it visible to all associated producers.
+		 */
+		smp_store_mb(cq->notify->flags, SIW_NOTIFY_SOLICITED);
 	else
-		/* CQ event for any signalled completion */
-		smp_store_mb(*cq->notify, SIW_NOTIFY_ALL);
+		/*
+		 * Enable CQ event for any signalled completion.
+		 * and make it visible to all associated producers.
+		 */
+		smp_store_mb(cq->notify->flags, SIW_NOTIFY_ALL);
 
 	if (flags & IB_CQ_REPORT_MISSED_EVENTS)
 		return cq->cq_put - cq->cq_get;

include/uapi/rdma/siw-abi.h

···
  * to control CQ arming.
  */
 struct siw_cq_ctrl {
-	__aligned_u64 notify;
+	__u32 flags;
+	__u32 pad;
 };
 #endif