[PATCH 1/3] dma-mapping: introduce the DMA_ATTR_NO_WARN attribute

[Tim Gardner]

From: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1633128

Introduce the DMA_ATTR_NO_WARN attribute, and document it.

Link: http://lkml.kernel.org/r/1470092390-25451-2-git-send-email-mauricfo@linux.vnet.ibm.com
Signed-off-by: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>
Cc: Keith Busch <keith.busch at intel.com>
Cc: Jens Axboe <axboe at fb.com>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Krzysztof Kozlowski <k.kozlowski at samsung.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(back ported from commit a9a62c9384417545620aee1b5ad1d9357350c17a)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>

 Conflicts:
	Documentation/DMA-attributes.txt
	include/linux/dma-mapping.h
---
 Documentation/DMA-attributes.txt | 43 ++++++++++++++++++++++++++++++++
 include/linux/dma-mapping.h      | 53 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 18dc52c..48150c6 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -100,3 +100,46 @@ allocated by dma_alloc_attrs() function from individual pages if it can
 be mapped as contiguous chunk into device dma address space. By
 specifying this attribute the allocated buffer is forced to be contiguous
 also in physical memory.
+
+DMA_ATTR_ALLOC_SINGLE_PAGES
+---------------------------
+
+This is a hint to the DMA-mapping subsystem that it's probably not worth
+the time to try to allocate memory to in a way that gives better TLB
+efficiency (AKA it's not worth trying to build the mapping out of larger
+pages).  You might want to specify this if:
+- You know that the accesses to this memory won't thrash the TLB.
+  You might know that the accesses are likely to be sequential or
+  that they aren't sequential but it's unlikely you'll ping-pong
+  between many addresses that are likely to be in different physical
+  pages.
+- You know that the penalty of TLB misses while accessing the
+  memory will be small enough to be inconsequential.  If you are
+  doing a heavy operation like decryption or decompression this
+  might be the case.
+- You know that the DMA mapping is fairly transitory.  If you expect
+  the mapping to have a short lifetime then it may be worth it to
+  optimize allocation (avoid coming up with large pages) instead of
+  getting the slight performance win of larger pages.
+Setting this hint doesn't guarantee that you won't get huge pages, but it
+means that we won't try quite as hard to get them.
+
+NOTE: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM,
+though ARM64 patches will likely be posted soon.
+
+DMA_ATTR_NO_WARN
+----------------
+
+This tells the DMA-mapping subsystem to suppress allocation failure reports
+(similarly to __GFP_NOWARN).
+
+On some architectures allocation failures are reported with error messages
+to the system logs.  Although this can help to identify and debug problems,
+drivers which handle failures (eg, retry later) have no problems with them,
+and can actually flood the system logs with error messages that aren't any
+problem at all, depending on the implementation of the retry mechanism.
+
+So, this provides a way for drivers to avoid those error messages on calls
+where allocation failures are not a problem, and shouldn't bother the logs.
+
+NOTE: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 2e551e2..c0658ce 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -8,6 +8,59 @@
 #include <linux/dma-attrs.h>
 #include <linux/dma-direction.h>
 #include <linux/scatterlist.h>
+#include <linux/kmemcheck.h>
+#include <linux/bug.h>
+
+/**
+ * List of possible attributes associated with a DMA mapping. The semantics
+ * of each attribute should be defined in Documentation/DMA-attributes.txt.
+ *
+ * DMA_ATTR_WRITE_BARRIER: DMA to a memory region with this attribute
+ * forces all pending DMA writes to complete.
+ */
+#define DMA_ATTR_WRITE_BARRIER		(1UL << 0)
+/*
+ * DMA_ATTR_WEAK_ORDERING: Specifies that reads and writes to the mapping
+ * may be weakly ordered, that is that reads and writes may pass each other.
+ */
+#define DMA_ATTR_WEAK_ORDERING		(1UL << 1)
+/*
+ * DMA_ATTR_WRITE_COMBINE: Specifies that writes to the mapping may be
+ * buffered to improve performance.
+ */
+#define DMA_ATTR_WRITE_COMBINE		(1UL << 2)
+/*
+ * DMA_ATTR_NON_CONSISTENT: Lets the platform to choose to return either
+ * consistent or non-consistent memory as it sees fit.
+ */
+#define DMA_ATTR_NON_CONSISTENT		(1UL << 3)
+/*
+ * DMA_ATTR_NO_KERNEL_MAPPING: Lets the platform to avoid creating a kernel
+ * virtual mapping for the allocated buffer.
+ */
+#define DMA_ATTR_NO_KERNEL_MAPPING	(1UL << 4)
+/*
+ * DMA_ATTR_SKIP_CPU_SYNC: Allows platform code to skip synchronization of
+ * the CPU cache for the given buffer assuming that it has been already
+ * transferred to 'device' domain.
+ */
+#define DMA_ATTR_SKIP_CPU_SYNC		(1UL << 5)
+/*
+ * DMA_ATTR_FORCE_CONTIGUOUS: Forces contiguous allocation of the buffer
+ * in physical memory.
+ */
+#define DMA_ATTR_FORCE_CONTIGUOUS	(1UL << 6)
+/*
+ * DMA_ATTR_ALLOC_SINGLE_PAGES: This is a hint to the DMA-mapping subsystem
+ * that it's probably not worth the time to try to allocate memory to in a way
+ * that gives better TLB efficiency.
+ */
+#define DMA_ATTR_ALLOC_SINGLE_PAGES	(1UL << 7)
+/*
+ * DMA_ATTR_NO_WARN: This tells the DMA-mapping subsystem to suppress
+ * allocation failure reports (similarly to __GFP_NOWARN).
+ */
+#define DMA_ATTR_NO_WARN	(1UL << 8)
 
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.
-- 
2.7.4