drm/radeon/kms: add retry limits for native DP aux defer

The previous code could potentially loop forever.  Limit
the number of DP aux defer retries to 4 for native aux
transactions, same as i2c over aux transactions.

Noticed by: Brad Campbell <lists2009@fnarfbargle.com>

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Brad Campbell <lists2009@fnarfbargle.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index f526fa77e32..4da23889fea 100644
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -115,6 +115,7 @@ static int radeon_dp_aux_native_write(struct radeon_connector *radeon_connector,
         u8 msg[20];
         int msg_bytes = send_bytes + 4;
         u8 ack;
+        unsigned retry;
 
         if (send_bytes > 16)
                 return -1;
@@ -125,20 +126,20 @@ static int radeon_dp_aux_native_write(struct radeon_connector *radeon_connector,
         msg[3] = (msg_bytes << 4) | (send_bytes - 1);
         memcpy(&msg[4], send, send_bytes);
 
-        while (1) {
+        for (retry = 0; retry < 4; retry++) {
                 ret = radeon_process_aux_ch(dig_connector->dp_i2c_bus,
                                             msg, msg_bytes, NULL, 0, delay, &ack);
                 if (ret < 0)
                         return ret;
                 if ((ack & AUX_NATIVE_REPLY_MASK) == AUX_NATIVE_REPLY_ACK)
-                        break;
+                        return send_bytes;
                 else if ((ack & AUX_NATIVE_REPLY_MASK) == AUX_NATIVE_REPLY_DEFER)
                         udelay(400);
                 else
                         return -EIO;
         }
 
-        return send_bytes;
+        return -EIO;
 }
 
 static int radeon_dp_aux_native_read(struct radeon_connector *radeon_connector,
@@ -149,13 +150,14 @@ static int radeon_dp_aux_native_read(struct radeon_connector *radeon_connector,
         int msg_bytes = 4;
         u8 ack;
         int ret;
+        unsigned retry;
 
         msg[0] = address;
         msg[1] = address >> 8;
         msg[2] = AUX_NATIVE_READ << 4;
         msg[3] = (msg_bytes << 4) | (recv_bytes - 1);
 
-        while (1) {
+        for (retry = 0; retry < 4; retry++) {
                 ret = radeon_process_aux_ch(dig_connector->dp_i2c_bus,
                                             msg, msg_bytes, recv, recv_bytes, delay, &ack);
                 if (ret < 0)
@@ -169,6 +171,8 @@ static int radeon_dp_aux_native_read(struct radeon_connector *radeon_connector,
                 else
                         return -EIO;
         }
+
+        return -EIO;
 }
 
 static void radeon_write_dpcd_reg(struct radeon_connector *radeon_connector,