[PATCH v6 6/9] i2c: smbus: use DMA safe buffers for emulated SMBus transactions

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

For all block commands, try to allocate a DMA safe buffer and mark it
accordingly. Only use the stack, if the buffers cannot be allocated.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/i2c-core-smbus.c | 45 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 4bb9927afd0106..931c274fe26809 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -18,6 +18,7 @@
 #include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/i2c-smbus.h>
+#include <linux/slab.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/smbus.h>
@@ -291,6 +292,22 @@ s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client, u8 command,
 }
 EXPORT_SYMBOL(i2c_smbus_write_i2c_block_data);
 
+static void i2c_smbus_try_get_dmabuf(struct i2c_msg *msg, u8 init_val)
+{
+	bool is_read = msg->flags & I2C_M_RD;
+	unsigned char *dma_buf;
+
+	dma_buf = kzalloc(I2C_SMBUS_BLOCK_MAX + (is_read ? 2 : 3), GFP_KERNEL);
+	if (!dma_buf)
+		return;
+
+	msg->buf = dma_buf;
+	msg->flags |= I2C_M_DMA_SAFE;
+
+	if (init_val)
+		msg->buf[0] = init_val;
+
+}
 /* Simulate a SMBus command using the i2c protocol
    No checking of parameters is done!  */
 static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
@@ -368,6 +385,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 			msg[1].flags |= I2C_M_RECV_LEN;
 			msg[1].len = 1; /* block length will be added by
 					   the underlying bus driver */
+			i2c_smbus_try_get_dmabuf(&msg[1], 0);
 		} else {
 			msg[0].len = data->block[0] + 2;
 			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 2) {
@@ -376,8 +394,10 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 					data->block[0]);
 				return -EINVAL;
 			}
+
+			i2c_smbus_try_get_dmabuf(&msg[0], command);
 			for (i = 1; i < msg[0].len; i++)
-				msgbuf0[i] = data->block[i-1];
+				msg[0].buf[i] = data->block[i-1];
 		}
 		break;
 	case I2C_SMBUS_BLOCK_PROC_CALL:
@@ -389,16 +409,21 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 				data->block[0]);
 			return -EINVAL;
 		}
+
 		msg[0].len = data->block[0] + 2;
+		i2c_smbus_try_get_dmabuf(&msg[0], command);
 		for (i = 1; i < msg[0].len; i++)
-			msgbuf0[i] = data->block[i-1];
+			msg[0].buf[i] = data->block[i-1];
+
 		msg[1].flags |= I2C_M_RECV_LEN;
 		msg[1].len = 1; /* block length will be added by
 				   the underlying bus driver */
+		i2c_smbus_try_get_dmabuf(&msg[1], 0);
 		break;
 	case I2C_SMBUS_I2C_BLOCK_DATA:
 		if (read_write == I2C_SMBUS_READ) {
 			msg[1].len = data->block[0];
+			i2c_smbus_try_get_dmabuf(&msg[1], 0);
 		} else {
 			msg[0].len = data->block[0] + 1;
 			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
@@ -407,8 +432,10 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 					data->block[0]);
 				return -EINVAL;
 			}
+
+			i2c_smbus_try_get_dmabuf(&msg[0], command);
 			for (i = 1; i <= data->block[0]; i++)
-				msgbuf0[i] = data->block[i];
+				msg[0].buf[i] = data->block[i];
 		}
 		break;
 	default:
@@ -456,14 +483,20 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
 			break;
 		case I2C_SMBUS_I2C_BLOCK_DATA:
 			for (i = 0; i < data->block[0]; i++)
-				data->block[i+1] = msgbuf1[i];
+				data->block[i+1] = msg[1].buf[i];
 			break;
 		case I2C_SMBUS_BLOCK_DATA:
 		case I2C_SMBUS_BLOCK_PROC_CALL:
-			for (i = 0; i < msgbuf1[0] + 1; i++)
-				data->block[i] = msgbuf1[i];
+			for (i = 0; i < msg[1].buf[0] + 1; i++)
+				data->block[i] = msg[1].buf[i];
 			break;
 		}
+
+	if (msg[0].flags & I2C_M_DMA_SAFE)
+		kfree(msg[0].buf);
+	if (msg[1].flags & I2C_M_DMA_SAFE)
+		kfree(msg[1].buf);
+
 	return 0;
 }
 
-- 
2.11.0