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>

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index f526fa7..4da2388 100644 (file)
--- 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,