One helper checks if DMA is suitable and optionally creates a bounce
buffer, if not. The other function returns the bounce buffer and makes
sure the data is properly copied back to the message.
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxxxxx>
---
include/linux/i2c.h | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 72d0ece70ed30d..7204d38eaff07c 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -33,7 +33,10 @@
#include <linux/rtmutex.h>
#include <linux/irqdomain.h> /* for Host Notify IRQ */
#include <linux/of.h> /* for struct device_node */
+#include <linux/slab.h>
#include <linux/swab.h> /* for swab16 */
+#include <linux/mm.h>
+#include <linux/sched/task_stack.h>
#include <uapi/linux/i2c.h>
extern struct bus_type i2c_bus_type;
@@ -764,6 +767,68 @@ static inline u8 i2c_8bit_addr_from_msg(const struct i2c_msg *msg)
return (msg->addr << 1) | (msg->flags & I2C_M_RD ? 1 : 0);
}
+/**
+ * i2c_check_msg_for_dma - check if a message is suitable for DMA
+ * @msg: the message to be checked
+ * @threshold: the amount of byte from which using DMA makes sense
+ * @ptr_for_bounce_buf: if not NULL, a bounce buffer will be attached to this
+ * ptr, if needed. The bounce buffer must be freed by the
+ * caller using i2c_release_bounce_buf().
+ *
+ * Return: -ERANGE if message is smaller than threshold
+ * -EFAULT if message buffer is not DMA capable and no bounce buffer
+ * was requested
+ * -ENOMEM if a bounce buffer could not be created
+ * 0 if message is suitable for DMA
+ *
+ * Note: This function should only be called from process context! It uses
+ * helper functions which work on the 'current' task.
+ */
+static inline int i2c_check_msg_for_dma(struct i2c_msg *msg, unsigned int threshold,
+ u8 **ptr_for_bounce_buf)
+{
+ if (ptr_for_bounce_buf)
+ *ptr_for_bounce_buf = NULL;
+
+ if (msg->len < threshold)
+ return -ERANGE;
+
+ if (!virt_addr_valid(msg->buf) || object_is_on_stack(msg->buf)) {
+ pr_debug("msg buffer to 0x%04x is not DMA safe%s\n", msg->addr,
+ ptr_for_bounce_buf ? ", trying bounce buffer" : "");
+ if (ptr_for_bounce_buf) {
+ if (msg->flags & I2C_M_RD)
+ *ptr_for_bounce_buf = kzalloc(msg->len, GFP_KERNEL);
+ else
+ *ptr_for_bounce_buf = kmemdup(msg->buf, msg->len,
+ GFP_KERNEL);
+ if (!*ptr_for_bounce_buf)
+ return -ENOMEM;
+ } else {
+ return -EFAULT;
+ }
+ }
+
+ return 0;
+}
+
+/**
+ * i2c_release_bounce_buf - copy data back from bounce buffer and release it
+ * @msg: the message to be copied back to
+ * @bounce_buf: the bounce buffer obtained from i2c_check_msg_for_dma().
+ * May be NULL.
+ */
+static inline void i2c_release_bounce_buf(struct i2c_msg *msg, u8 *bounce_buf)
+{
+ if (!bounce_buf)
+ return;
+
+ if (msg->flags & I2C_M_RD)
+ memcpy(msg->buf, bounce_buf, msg->len);
+
+ kfree(bounce_buf);
+}
+
int i2c_handle_smbus_host_notify(struct i2c_adapter *adap, unsigned short addr);
/**
* module_i2c_driver() - Helper macro for registering a modular I2C driver
--
2.11.0
--
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