[U-Boot] [PATCH] I2C: OMAP: detect more devices when probing an i2c bus

[Nick Thompson]

The omap24xx driver only seems to support devices that have a single subaddress
byte. With these types of devices, the first access in a bus transaction is
usually a write (writes the subaddress) followed by either a read or write to
access the devices registers.

Many such devices will respond to a read as the first access, but there are at
least some that will NACK such a read. (e.g. ADV7180.)

The probe function attempts to detect a devices ACK to a read access only and
fails to find devices that NACK a read.

This commit modifies the probe function to start a write instead. This detects
devices that respond to reads (since they must also respond to writes) as well
as those that only respond to writes. The bus is immediately set to idle after a
(N)ACK avoiding actually writing anything to the device.

Signed-off-by: Nick Thompson <nick.thompson at ge.com>
---
Tested on OMAP3530 with an ADV7180 video ADC.

Detection of a device takes the same time as failing to find a device, so the
probe is slightly faster.

 drivers/i2c/omap24xx_i2c.c |   42 +++++++++++-------------------------------
 1 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/drivers/i2c/omap24xx_i2c.c b/drivers/i2c/omap24xx_i2c.c
index 215be34..bc637bc 100644
--- a/drivers/i2c/omap24xx_i2c.c
+++ b/drivers/i2c/omap24xx_i2c.c
@@ -321,43 +321,23 @@ int i2c_probe (uchar chip)
     /* wait until bus not busy */
     wait_for_bb ();
 
-    /* try to read one byte */
+    /* try to write one byte */
     writew (1, &i2c_base->cnt);
     /* set slave address */
     writew (chip, &i2c_base->sa);
     /* stop bit needed here */
-    writew (I2C_CON_EN | I2C_CON_MST | I2C_CON_STT | I2C_CON_STP, &i2c_base->con);
+    writew (I2C_CON_EN | I2C_CON_MST | I2C_CON_STT | I2C_CON_TRX |
+        I2C_CON_STP, &i2c_base->con);
 
-    while (1) {
-        status = wait_for_pin();
-        if (status == 0 || status & I2C_STAT_AL) {
-            res = 1;
-            goto probe_exit;
-        }
-        if (status & I2C_STAT_NACK) {
-            res = 1;
-            writew(0xff, &i2c_base->stat);
-            writew (readw (&i2c_base->con) | I2C_CON_STP, &i2c_base->con);
-            wait_for_bb ();
-            break;
-        }
-        if (status & I2C_STAT_ARDY) {
-            writew(I2C_STAT_ARDY, &i2c_base->stat);
-            break;
-        }
-        if (status & I2C_STAT_RRDY) {
-            res = 0;
-#if defined(CONFIG_OMAP243X) || defined(CONFIG_OMAP34XX) || \
-    defined(CONFIG_OMAP44XX)
-            readb(&i2c_base->data);
-#else
-            readw(&i2c_base->data);
-#endif
-            writew(I2C_STAT_RRDY, &i2c_base->stat);
-        }
-    }
+    status = wait_for_pin();
+
+    /* check for ACK (!NAK) */
+    if (!(status & I2C_STAT_NACK))
+        res = 0;
+
+    /* abort transfer (force idle state) */
+    writew (0, &i2c_base->con);
 
-probe_exit:
     flush_fifo();
     writew (0, &i2c_base->cnt); /* don't allow any more data in...we don't want it.*/
     writew(0xFFFF, &i2c_base->stat);
-- 
1.7.1