[PATCH v2 RESEND 3/7] dma-mapping: introduce the DMA_ATTR_MAY_SLEEP attribute

[Petr Tesarik]

From: Petr Tesarik <petr.tesarik.ext at huawei.com>

Introduce a DMA attribute to tell the DMA-mapping subsystem that
the operation is allowed to sleep.

This patch merely adds the flag, but it does not do anything at
the moment.

Signed-off-by: Petr Tesarik <petr.tesarik.ext at huawei.com>
---
 Documentation/core-api/dma-attributes.rst | 10 ++++++++++
 include/linux/dma-mapping.h               |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
index 1887d92e8e92..9ce00926455f 100644
--- a/Documentation/core-api/dma-attributes.rst
+++ b/Documentation/core-api/dma-attributes.rst
@@ -130,3 +130,13 @@ accesses to DMA buffers in both privileged "supervisor" and unprivileged
 subsystem that the buffer is fully accessible at the elevated privilege
 level (and ideally inaccessible or at least read-only at the
 lesser-privileged levels).
+
+DMA_ATTR_MAY_SLEEP
+------------------
+
+This tells the DMA-mapping subsystem that it is allowed to sleep. For example,
+if mapping needs a bounce buffer, software IO TLB may use CMA for the
+allocation if this flag is given.
+
+This attribute is not used for dma_alloc\* functions. Instead, the provided
+GFP flags are used to determine whether the allocation may sleep.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 0ee20b764000..7a75c503ac38 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -61,6 +61,12 @@
  */
 #define DMA_ATTR_PRIVILEGED		(1UL << 9)
 
+/*
+ * DMA_ATTR_MAY_SLEEP: This tells the DMA-mapping subsystem that it is allowed
+ * to sleep.
+ */
+#define DMA_ATTR_MAY_SLEEP		(1UL << 10)
+
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
  * be given to a device to use as a DMA source or target.  It is specific to a
-- 
2.25.1