i2c: img-scb: support I2C_M_IGNORE_NAK

This commit adds support for the I2C_M_IGNORE_NAK protocol
modification.

Such behaviour can only be implemented in atomic mode. So, if a
transaction contains a message with such flag the drivers
switches to atomic mode. The implementation consists simply in
treating NAKs as ACKs.

Signed-off-by: Sifan Naeem <sifan.naeem@imgtec.com>
Acked-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: James Hartley <james.hartley@imgtec.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-img-scb.c b/drivers/i2c/busses/i2c-img-scb.c
index 3795fe1..c92bcf7 100644 (file)
--- a/drivers/i2c/busses/i2c-img-scb.c
+++ b/drivers/i2c/busses/i2c-img-scb.c
@@ -750,7 +750,9 @@ static unsigned int img_i2c_atomic(struct img_i2c *i2c,
                        next_cmd = CMD_RET_ACK;
                break;
        case CMD_RET_ACK:
-               if (i2c->line_status & LINESTAT_ACK_DET) {
+               if (i2c->line_status & LINESTAT_ACK_DET ||
+                   (i2c->line_status & LINESTAT_NACK_DET &&
+                   i2c->msg.flags & I2C_M_IGNORE_NAK)) {
                        if (i2c->msg.len == 0) {
                                next_cmd = CMD_GEN_STOP;
                        } else if (i2c->msg.flags & I2C_M_RD) {
@@ -1017,20 +1019,23 @@ static int img_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
                return -EIO;
 
        for (i = 0; i < num; i++) {
-               if (likely(msgs[i].len))
-                       continue;
                /*
                 * 0 byte reads are not possible because the slave could try
                 * and pull the data line low, preventing a stop bit.
                 */
-               if (unlikely(msgs[i].flags & I2C_M_RD))
+               if (!msgs[i].len && msgs[i].flags & I2C_M_RD)
                        return -EIO;
                /*
                 * 0 byte writes are possible and used for probing, but we
                 * cannot do them in automatic mode, so use atomic mode
                 * instead.
+                *
+                * Also, the I2C_M_IGNORE_NAK mode can only be implemented
+                * in atomic mode.
                 */
-               atomic = true;
+               if (!msgs[i].len ||
+                   (msgs[i].flags & I2C_M_IGNORE_NAK))
+                       atomic = true;
        }
 
        ret = clk_prepare_enable(i2c->scb_clk);