1 files changed, 35 insertions, 20 deletions

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 27671489477d..4b6e6f3ba0a1 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -577,7 +577,9 @@ static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
 
 /*
  * Transfer a single I2C-over-AUX message and handle various error conditions,
- * retrying the transaction as appropriate.
+ * retrying the transaction as appropriate.  It is assumed that the
+ * aux->transfer function does not modify anything in the msg other than the
+ * reply field.
  */
 static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 {
@@ -665,11 +667,26 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 {
         struct drm_dp_aux *aux = adapter->algo_data;
         unsigned int i, j;
+        struct drm_dp_aux_msg msg;
+        int err = 0;
 
-        for (i = 0; i < num; i++) {
-                struct drm_dp_aux_msg msg;
-                int err;
+        memset(&msg, 0, sizeof(msg));
 
+        for (i = 0; i < num; i++) {
+                msg.address = msgs[i].addr;
+                msg.request = (msgs[i].flags & I2C_M_RD) ?
+                        DP_AUX_I2C_READ :
+                        DP_AUX_I2C_WRITE;
+                msg.request |= DP_AUX_I2C_MOT;
+                /* Send a bare address packet to start the transaction.
+                 * Zero sized messages specify an address only (bare
+                 * address) transaction.
+                 */
+                msg.buffer = NULL;
+                msg.size = 0;
+                err = drm_dp_i2c_do_msg(aux, &msg);
+                if (err < 0)
+                        break;
                 /*
                  * Many hardware implementations support FIFOs larger than a
                  * single byte, but it has been empirically determined that
@@ -678,30 +695,28 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
                  * transferred byte-by-byte.
                  */
                 for (j = 0; j < msgs[i].len; j++) {
-                        memset(&msg, 0, sizeof(msg));
-                        msg.address = msgs[i].addr;
-
-                        msg.request = (msgs[i].flags & I2C_M_RD) ?
-                                        DP_AUX_I2C_READ :
-                                        DP_AUX_I2C_WRITE;
-
-                        /*
-                         * All messages except the last one are middle-of-
-                         * transfer messages.
-                         */
-                        if ((i < num - 1) || (j < msgs[i].len - 1))
-                                msg.request |= DP_AUX_I2C_MOT;
-
                         msg.buffer = msgs[i].buf + j;
                         msg.size = 1;
 
                         err = drm_dp_i2c_do_msg(aux, &msg);
                         if (err < 0)
-                                return err;
+                                break;
                 }
+                if (err < 0)
+                        break;
         }
+        if (err >= 0)
+                err = num;
+        /* Send a bare address packet to close out the transaction.
+         * Zero sized messages specify an address only (bare
+         * address) transaction.
+         */
+        msg.request &= ~DP_AUX_I2C_MOT;
+        msg.buffer = NULL;
+        msg.size = 0;
+        (void)drm_dp_i2c_do_msg(aux, &msg);
 
-        return num;
+        return err;
 }
 
 static const struct i2c_algorithm drm_dp_i2c_algo = {