drm/i915/dp: add native aux defer retry limit

commit f51a44b9a6c4982cc25bfb3727de9bb893621ebc upstream.

Retrying indefinitely places too much trust on the aux implementation of
the sink devices.

Reported-by: Daniel Martin <consume.noise@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71267
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Theodore Ts'o <tytso@mit.edu>
Tested-by: Sree Harsha Totakura <freedesktop@h.totakura.in>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 39849a9..ca75076 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -483,6 +483,7 @@ intel_dp_aux_native_write(struct intel_dp *intel_dp,
        uint8_t msg[20];
        int msg_bytes;
        uint8_t ack;
+       int retry;
 
        intel_dp_check_edp(intel_dp);
        if (send_bytes > 16)
@@ -493,18 +494,20 @@ intel_dp_aux_native_write(struct intel_dp *intel_dp,
        msg[3] = send_bytes - 1;
        memcpy(&msg[4], send, send_bytes);
        msg_bytes = send_bytes + 4;
-       for (;;) {
+       for (retry = 0; retry < 7; retry++) {
                ret = intel_dp_aux_ch(intel_dp, msg, msg_bytes, &ack, 1);
                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)
                        usleep_range(400, 500);
                else
                        return -EIO;
        }
-       return send_bytes;
+
+       DRM_ERROR("too many retries, giving up\n");
+       return -EIO;
 }
 
 /* Write a single byte to the aux channel in native mode */
@@ -526,6 +529,7 @@ intel_dp_aux_native_read(struct intel_dp *intel_dp,
        int reply_bytes;
        uint8_t ack;
        int ret;
+       int retry;
 
        intel_dp_check_edp(intel_dp);
        msg[0] = AUX_NATIVE_READ << 4;
@@ -536,7 +540,7 @@ intel_dp_aux_native_read(struct intel_dp *intel_dp,
        msg_bytes = 4;
        reply_bytes = recv_bytes + 1;
 
-       for (;;) {
+       for (retry = 0; retry < 7; retry++) {
                ret = intel_dp_aux_ch(intel_dp, msg, msg_bytes,
                                      reply, reply_bytes);
                if (ret == 0)
@@ -553,6 +557,9 @@ intel_dp_aux_native_read(struct intel_dp *intel_dp,
                else
                        return -EIO;
        }
+
+       DRM_ERROR("too many retries, giving up\n");
+       return -EIO;
 }
 
 static int