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

Wolfram Sang
2017-11-04T20:20:06Z

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