target/linux/brcm2708/patches-3.14/0018-Perform-I2C-combined-transactions-when-possible.patch

   1 From d002a24f7ff4ca8b63d08e33fd2d88af84501267 Mon Sep 17 00:00:00 2001
   2 From: cbeytas <cbeytas@shaw.ca>
   3 Date: Mon, 24 Jun 2013 00:05:40 -0400
   4 Subject: [PATCH 18/54] Perform I2C combined transactions when possible
   5
   6 Perform I2C combined transactions whenever possible, within the
   7 restrictions of the Broadcomm Serial Controller.
   8
   9 Disable DONE interrupt during TA poll
  10
  11 Prevent interrupt from being triggered if poll is missed and transfer
  12 starts and finishes.
  13
  14 i2c: Make combined transactions optional and disabled by default
  15 ---
  16  drivers/i2c/busses/i2c-bcm2708.c | 31 ++++++++++++++++++++++++++++++-
  17  1 file changed, 30 insertions(+), 1 deletion(-)
  18
  19 --- a/drivers/i2c/busses/i2c-bcm2708.c
  20 +++ b/drivers/i2c/busses/i2c-bcm2708.c
  21 @@ -74,6 +74,9 @@ static unsigned int baudrate = CONFIG_I2
  22  module_param(baudrate, uint, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
  23  MODULE_PARM_DESC(baudrate, "The I2C baudrate");
  24
  25 +static bool combined = false;
  26 +module_param(combined, bool, 0644);
  27 +MODULE_PARM_DESC(combined, "Use combined transactions");
  28
  29  struct bcm2708_i2c {
  30         struct i2c_adapter adapter;
  31 @@ -150,7 +153,7 @@ static inline void bcm2708_bsc_fifo_fill
  32  static inline void bcm2708_bsc_setup(struct bcm2708_i2c *bi)
  33  {
  34         unsigned long bus_hz;
  35 -       u32 cdiv;
  36 +       u32 cdiv, s;
  37         u32 c = BSC_C_I2CEN | BSC_C_INTD | BSC_C_ST | BSC_C_CLEAR_1;
  38
  39         bus_hz = clk_get_rate(bi->clk);
  40 @@ -166,6 +169,32 @@ static inline void bcm2708_bsc_setup(str
  41         bcm2708_wr(bi, BSC_DIV, cdiv);
  42         bcm2708_wr(bi, BSC_A, bi->msg->addr);
  43         bcm2708_wr(bi, BSC_DLEN, bi->msg->len);
  44 +       if (combined)
  45 +       {
  46 +               /* Do the next two messages meet combined transaction criteria?
  47 +                  - Current message is a write, next message is a read
  48 +                  - Both messages to same slave address
  49 +                  - Write message can fit inside FIFO (16 bytes or less) */
  50 +               if ( (bi->nmsgs > 1) &&
  51 +                   !(bi->msg[0].flags & I2C_M_RD) && (bi->msg[1].flags & I2C_M_RD) &&
  52 +                    (bi->msg[0].addr == bi->msg[1].addr) && (bi->msg[0].len <= 16)) {
  53 +                       /* Fill FIFO with entire write message (16 byte FIFO) */
  54 +                       while (bi->pos < bi->msg->len)
  55 +                               bcm2708_wr(bi, BSC_FIFO, bi->msg->buf[bi->pos++]);
  56 +                       /* Start write transfer (no interrupts, don't clear FIFO) */
  57 +                       bcm2708_wr(bi, BSC_C, BSC_C_I2CEN | BSC_C_ST);
  58 +                       /* poll for transfer start bit (should only take 1-20 polls) */
  59 +                       do {
  60 +                               s = bcm2708_rd(bi, BSC_S);
  61 +                       } while (!(s & (BSC_S_TA | BSC_S_ERR | BSC_S_CLKT | BSC_S_DONE)));
  62 +                       /* Send next read message before the write transfer finishes. */
  63 +                       bi->nmsgs--;
  64 +                       bi->msg++;
  65 +                       bi->pos = 0;
  66 +                       bcm2708_wr(bi, BSC_DLEN, bi->msg->len);
  67 +                       c = BSC_C_I2CEN | BSC_C_INTD | BSC_C_INTR | BSC_C_ST | BSC_C_READ;
  68 +               }
  69 +       }
  70         bcm2708_wr(bi, BSC_C, c);
  71  }
  72