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Subject[PATCH RFC v2 12/14] dmaengine: request submit optimization
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Date
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@intel.com>
---
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
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