i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
  TXD: is set when the FIFO has space for at least one byte of data.
  RXD: is set when the FIFO contains at least one byte of data.
  TXW: is set during a write transfer and the FIFO is less than full.
  RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index d4f3239b56865919e1b781b20a7c5ebcd76b4eb9..f283b714aa79e2e4685ed95b04b6b289f7e9eee7 100644 (file)
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -64,6 +64,7 @@ struct bcm2835_i2c_dev {
        int irq;
        struct i2c_adapter adapter;
        struct completion completion;
+       struct i2c_msg *curr_msg;
        u32 msg_err;
        u8 *msg_buf;
        size_t msg_buf_remaining;
@@ -126,14 +127,13 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
                return IRQ_HANDLED;
        }
 
-       if (val & BCM2835_I2C_S_RXD) {
-               bcm2835_drain_rxfifo(i2c_dev);
-               if (!(val & BCM2835_I2C_S_DONE))
-                       return IRQ_HANDLED;
-       }
-
        if (val & BCM2835_I2C_S_DONE) {
-               if (i2c_dev->msg_buf_remaining)
+               if (i2c_dev->curr_msg->flags & I2C_M_RD) {
+                       bcm2835_drain_rxfifo(i2c_dev);
+                       val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+               }
+
+               if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
                        i2c_dev->msg_err = BCM2835_I2C_S_LEN;
                else
                        i2c_dev->msg_err = 0;
@@ -141,11 +141,16 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
                return IRQ_HANDLED;
        }
 
-       if (val & BCM2835_I2C_S_TXD) {
+       if (val & BCM2835_I2C_S_TXW) {
                bcm2835_fill_txfifo(i2c_dev);
                return IRQ_HANDLED;
        }
 
+       if (val & BCM2835_I2C_S_RXR) {
+               bcm2835_drain_rxfifo(i2c_dev);
+               return IRQ_HANDLED;
+       }
+
        return IRQ_NONE;
 }
 
@@ -155,6 +160,7 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
        u32 c;
        unsigned long time_left;
 
+       i2c_dev->curr_msg = msg;
        i2c_dev->msg_buf = msg->buf;
        i2c_dev->msg_buf_remaining = msg->len;
        reinit_completion(&i2c_dev->completion);