ps8640_aux_transfer_msg() programs the AUX address registers, starts the
AUX transfer, waits for SWAUX_SEND to clear, and reads the AUX status
register. Several of those regmap operations have return values, but the
function only checks a stale ret after the status read.

Propagate failures from the address write, transfer start, completion
poll, and status read. This avoids returning a transfer length when the
bridge register transaction or AUX completion wait failed.

Fixes: 13afcdd7277e ("drm/bridge: parade-ps8640: Add support for AUX channel")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
Changes since v1: https://lore.kernel.org/all/20260623060635.16064-1-pengpeng@iscas.ac.cn/
- include the AUX address and length in the address-write diagnostic
- describe poll failures without assuming that every error is a timeout
- add the Fixes tag suggested by Doug
- rebase onto the current drm-misc-next tree

 drivers/gpu/drm/bridge/parade-ps8640.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index 96332721cb69..56b48f8feab6 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -257,8 +257,14 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux,
 	addr_len[PAGE0_SWAUX_LENGTH - base] = (len == 0) ? SWAUX_NO_PAYLOAD :
 					      ((len - 1) & SWAUX_LENGTH_MASK);
 
-	regmap_bulk_write(map, PAGE0_SWAUX_ADDR_7_0, addr_len,
-			  ARRAY_SIZE(addr_len));
+	ret = regmap_bulk_write(map, PAGE0_SWAUX_ADDR_7_0, addr_len,
+				ARRAY_SIZE(addr_len));
+	if (ret) {
+		DRM_DEV_ERROR(dev,
+			      "failed to write AUX address %#x, len %zu: %d\n",
+			      msg->address, len, ret);
+		return ret;
+	}
 
 	if (len && (request == DP_AUX_NATIVE_WRITE ||
 		    request == DP_AUX_I2C_WRITE)) {
@@ -274,13 +280,22 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux,
 		}
 	}
 
-	regmap_write(map, PAGE0_SWAUX_CTRL, SWAUX_SEND);
+	ret = regmap_write(map, PAGE0_SWAUX_CTRL, SWAUX_SEND);
+	if (ret) {
+		DRM_DEV_ERROR(dev, "failed to start AUX transfer: %d\n", ret);
+		return ret;
+	}
 
 	/* Zero delay loop because i2c transactions are slow already */
-	regmap_read_poll_timeout(map, PAGE0_SWAUX_CTRL, data,
-				 !(data & SWAUX_SEND), 0, 50 * 1000);
+	ret = regmap_read_poll_timeout(map, PAGE0_SWAUX_CTRL, data,
+				       !(data & SWAUX_SEND), 0, 50 * 1000);
+	if (ret) {
+		DRM_DEV_ERROR(dev, "failed to complete AUX transfer: %d\n",
+			      ret);
+		return ret;
+	}
 
-	regmap_read(map, PAGE0_SWAUX_STATUS, &data);
+	ret = regmap_read(map, PAGE0_SWAUX_STATUS, &data);
 	if (ret) {
 		DRM_DEV_ERROR(dev, "failed to read PAGE0_SWAUX_STATUS: %d\n",
 			      ret);
-- 
2.50.1 (Apple Git-155)