linux-kernel - [RFC PATCH v4 1/6] i2c: add a message flag for DMA safe buffers

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Date:   Thu, 17 Aug 2017 16:14:44 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     linux-i2c@...r.kernel.org
Cc:     linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-input@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: [RFC PATCH v4 1/6] i2c: add a message flag for DMA safe buffers

I2C has no requirement that the buffer of a message needs to be DMA
safe. In case it is, it can now be flagged, so drivers wishing to
do DMA can use the buffer directly.

Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
---
 include/uapi/linux/i2c.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/uapi/linux/i2c.h b/include/uapi/linux/i2c.h
index 009e27bb9abe19..1c683cb319e4b7 100644
--- a/include/uapi/linux/i2c.h
+++ b/include/uapi/linux/i2c.h
@@ -71,6 +71,9 @@ struct i2c_msg {
 #define I2C_M_RD		0x0001	/* read data, from slave to master */
 					/* I2C_M_RD is guaranteed to be 0x0001! */
 #define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
+#define I2C_M_DMA_SAFE		0x0200	/* the buffer of this message is DMA safe */
+					/* makes only sense in kernelspace */
+					/* userspace buffers are copied anyway */
 #define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */
 #define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
 #define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-- 
2.11.0