[PATCH RFC v2 12/14] dmaengine: request submit optimization

[Dave Jiang]

Adding dsa direct call to dmaengine for optimization. Spectre-v2 makes
indirect branches expensive. Adding direct call to the driver in order
to mitigate that and reduce cycles to initiate a descriptor submit.

Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
---
 drivers/dma/idxd/dma.c    |    5 +++--
 include/linux/dmaengine.h |    6 +++++-
 include/linux/idxd.h      |   20 ++++++++++++++++++++
 usr/include/Makefile      |    1 +
 4 files changed, 29 insertions(+), 3 deletions(-)
 create mode 100644 include/linux/idxd.h

diff --git a/drivers/dma/idxd/dma.c b/drivers/dma/idxd/dma.c
index 07fbc98668ae..b9b4621e504a 100644
--- a/drivers/dma/idxd/dma.c
+++ b/drivers/dma/idxd/dma.c
@@ -8,6 +8,7 @@
 #include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/dmaengine.h>
 #include <uapi/linux/idxd.h>
+#include <linux/idxd.h>
 #include "../dmaengine.h"
 #include "registers.h"
 #include "idxd.h"
@@ -29,8 +30,7 @@ void idxd_parse_completion_status(u8 status, enum dmaengine_tx_result *res)
 	}
 }
 
-static int idxd_dma_submit_request(struct dma_chan *chan,
-				   struct dma_request *req)
+int idxd_dma_submit_request(struct dma_chan *chan, struct dma_request *req)
 {
 	struct idxd_wq *wq = container_of(chan, struct idxd_wq, dma_chan);
 
@@ -39,6 +39,7 @@ static int idxd_dma_submit_request(struct dma_chan *chan,
 
 	return -EINVAL;
 }
+EXPORT_SYMBOL_GPL(idxd_dma_submit_request);
 
 static int idxd_dma_alloc_chan_resources(struct dma_chan *chan)
 {
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 220d241d71ed..cebfa8db60a0 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -1395,6 +1395,7 @@ static inline int dma_get_slave_caps(struct dma_chan *chan,
 }
 #endif
 
+#include <linux/idxd.h>
 /* dmaengine_submit_request - helper routine for caller to submit
  *				a DMA request.
  * @chan: dma channel context
@@ -1412,7 +1413,10 @@ static inline int dmaengine_submit_request(struct dma_chan *chan,
 	if (!ddev->device_submit_request)
 		return -EINVAL;
 
-	return ddev->device_submit_request(chan, req);
+	if (ddev->device_submit_request == idxd_dma_submit_request)
+		return idxd_dma_submit_request(chan, req);
+	else
+		return ddev->device_submit_request(chan, req);
 }
 
 /* dmaengine_submit_request_and_wait - helper routine for caller to submit
diff --git a/include/linux/idxd.h b/include/linux/idxd.h
new file mode 100644
index 000000000000..4fb26d41a684
--- /dev/null
+++ b/include/linux/idxd.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2019 Intel Corporation. All rights rsvd. */
+#ifndef _LINUX_IDXD_H_
+#define _LINUX_IDXD_H_
+
+struct dmaengine_result;
+struct dma_request;
+struct dma_chan;
+
+#if IS_ENABLED(CONFIG_INTEL_IDXD)
+int idxd_dma_submit_request(struct dma_chan *chan, struct dma_request *req);
+#else
+static inline int idxd_dma_submit_request(struct dma_chan *chan,
+					  struct dma_request *req)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+#endif
diff --git a/usr/include/Makefile b/usr/include/Makefile
index 4a753a48767b..8bfd68bbc777 100644
--- a/usr/include/Makefile
+++ b/usr/include/Makefile
@@ -24,6 +24,7 @@ header-test- += linux/am437x-vpfe.h
 header-test- += linux/android/binder.h
 header-test- += linux/android/binderfs.h
 header-test- += linux/coda.h
+header-test- += linux/iadx.h
 header-test- += linux/elfcore.h
 header-test- += linux/errqueue.h
 header-test- += linux/fsmap.h