On Wed, Apr 11, 2012 at 5:05 PM, Henrik Rydberg [off-list ref] wrote:

Hi Daniel,

quoted

The i2c bus requires 5 bytes to do a 1 byte read (1-byte i2c address + 2
byte offset + 1-byte i2c address + 1 byte data), or 4 bytes to do a
1-byte write (1 byte i2c address + 2 byte offset + 1 byte data).

By taking a length with reads and writes, the driver can amortize
transaction overhead by performing larger transactions where
appropriate.

This patch just sets up the new API.  Later patches refactor
reads/writes
to take advantage of the larger transactions.

Signed-off-by: Daniel Kurtz <redacted>
Reviewed-by: Joonyoung Shim <redacted>
---
 drivers/input/touchscreen/atmel_mxt_ts.c |   47
+++++++++++++----------------
 1 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c

b/drivers/input/touchscreen/atmel_mxt_ts.c
index 15ae6fd..971f9dc 100644

--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c

@@ -397,8 +397,7 @@ static int mxt_fw_write(struct i2c_client *client,

      return 0;
 }

-static int __mxt_read_reg(struct i2c_client *client,
-                            u16 reg, u16 len, void *val)
+static int mxt_read_reg(struct i2c_client *client, u16 reg, u16 len,
void *val)
 {
      struct i2c_msg xfer[2];
      u8 buf[2];

@@ -419,28 +418,25 @@ static int __mxt_read_reg(struct i2c_client

*client,
      xfer[1].buf = val;

      if (i2c_transfer(client->adapter, xfer, 2) != 2) {
-             dev_err(&client->dev, "%s: i2c transfer failed\n",
__func__);
+             dev_err(&client->dev, "%s: i2c read failed\n", __func__);
              return -EIO;
      }

      return 0;
 }

-static int mxt_read_reg(struct i2c_client *client, u16 reg, u8 *val)
+static int mxt_write_reg(struct i2c_client *client, u16 reg, u16 len,
+                      const void *val)
 {
-     return __mxt_read_reg(client, reg, 1, val);
-}
-
-static int mxt_write_reg(struct i2c_client *client, u16 reg, u8 val)
-{
-     u8 buf[3];
+     size_t count = 2 + len;         /* + 2-byte offset */
+     u8 buf[count];

How much stack space are you planning to use here?

I missed this one when removing the other stack allocated array since
they are (rightly) frowned upon in the kernel.  I will replace with a
malloc, unless you have a better suggestion?

quoted

      buf[0] = reg & 0xff;
      buf[1] = (reg >> 8) & 0xff;
-     buf[2] = val;
+     memcpy(&buf[2], val, len);

-     if (i2c_master_send(client, buf, 3) != 3) {
-             dev_err(&client->dev, "%s: i2c send failed\n", __func__);
+     if (i2c_master_send(client, buf, count) != count) {
+             dev_err(&client->dev, "%s: i2c write failed\n", __func__);
              return -EIO;
      }

@@ -450,8 +446,7 @@ static int mxt_write_reg(struct i2c_client *client,

u16 reg, u8 val)
 static int mxt_read_object_table(struct i2c_client *client,
                                    u16 reg, u8 *object_buf)
 {
-     return __mxt_read_reg(client, reg, MXT_OBJECT_SIZE,
-                                object_buf);
+     return mxt_read_reg(client, reg, MXT_OBJECT_SIZE, object_buf);
 }

 static struct mxt_object *

@@ -481,8 +476,8 @@ static int mxt_read_message(struct mxt_data *data,

              return -EINVAL;

      reg = object->start_address;
-     return __mxt_read_reg(data->client, reg,
-                     sizeof(struct mxt_message), message);
+     return mxt_read_reg(data->client, reg, sizeof(struct mxt_message),
+                         message);
 }

 static int mxt_read_object(struct mxt_data *data,

@@ -496,7 +491,7 @@ static int mxt_read_object(struct mxt_data *data,

              return -EINVAL;

      reg = object->start_address;
-     return __mxt_read_reg(data->client, reg + offset, 1, val);
+     return mxt_read_reg(data->client, reg + offset, 1, val);
 }

 static int mxt_write_object(struct mxt_data *data,

@@ -510,7 +505,7 @@ static int mxt_write_object(struct mxt_data *data,

              return -EINVAL;

      reg = object->start_address;
-     return mxt_write_reg(data->client, reg + offset, val);
+     return mxt_write_reg(data->client, reg + offset, 1, &val);
 }

 static void mxt_input_report(struct mxt_data *data, int single_id)

@@ -757,27 +752,27 @@ static int mxt_get_info(struct mxt_data *data)

      int error;
      u8 val;

-     error = mxt_read_reg(client, MXT_FAMILY_ID, &val);
+     error = mxt_read_reg(client, MXT_FAMILY_ID, 1, &val);
      if (error)
              return error;
      info->family_id = val;

-     error = mxt_read_reg(client, MXT_VARIANT_ID, &val);
+     error = mxt_read_reg(client, MXT_VARIANT_ID, 1, &val);
      if (error)
              return error;
      info->variant_id = val;

-     error = mxt_read_reg(client, MXT_VERSION, &val);
+     error = mxt_read_reg(client, MXT_VERSION, 1, &val);
      if (error)
              return error;
      info->version = val;

-     error = mxt_read_reg(client, MXT_BUILD, &val);
+     error = mxt_read_reg(client, MXT_BUILD, 1, &val);
      if (error)
              return error;
      info->build = val;

-     error = mxt_read_reg(client, MXT_OBJECT_NUM, &val);
+     error = mxt_read_reg(client, MXT_OBJECT_NUM, 1, &val);
      if (error)
              return error;
      info->object_num = val;

@@ -860,12 +855,12 @@ static int mxt_initialize(struct mxt_data *data)

      msleep(MXT_RESET_TIME);

      /* Update matrix size at info struct */
-     error = mxt_read_reg(client, MXT_MATRIX_X_SIZE, &val);
+     error = mxt_read_reg(client, MXT_MATRIX_X_SIZE, 1, &val);
      if (error)
              return error;
      info->matrix_xsize = val;

-     error = mxt_read_reg(client, MXT_MATRIX_Y_SIZE, &val);
+     error = mxt_read_reg(client, MXT_MATRIX_Y_SIZE, 1, &val);
      if (error)
              return error;
      info->matrix_ysize = val;
--
1.7.7.3

Thanks,
Henrik

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