[PATCH 4/4] drm/bridge: ti-sn65dsi86: Update reply on aux failures

[Stephen Boyd]

We should be setting the drm_dp_aux_msg::reply field if a NACK or a
SHORT reply happens. Update the error bit handling logic in
ti_sn_aux_transfer() to handle these cases and notify upper layers that
such errors have happened. This helps the retry logic understand that a
timeout has happened, or to shorten the read length if the panel isn't
able to handle the longest read possible.

Cc: Douglas Anderson <dianders at chromium.org>
Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
Cc: Jonas Karlman <jonas at kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec at siol.net>
Cc: Sean Paul <seanpaul at chromium.org>
Signed-off-by: Stephen Boyd <swboyd at chromium.org>
---
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 31 +++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 6b6e98ca2881..19737bc01b8f 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -878,6 +878,7 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	case DP_AUX_NATIVE_READ:
 	case DP_AUX_I2C_READ:
 		regmap_write(pdata->regmap, SN_AUX_CMD_REG, request_val);
+		msg->reply = 0; /* Assume it's good */
 		break;
 	default:
 		return -EINVAL;
@@ -909,10 +910,32 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	ret = regmap_read(pdata->regmap, SN_AUX_CMD_STATUS_REG, &val);
 	if (ret)
 		return ret;
-	else if ((val & AUX_IRQ_STATUS_NAT_I2C_FAIL)
-		 || (val & AUX_IRQ_STATUS_AUX_RPLY_TOUT)
-		 || (val & AUX_IRQ_STATUS_AUX_SHORT))
-		return -ENXIO;
+
+	if (val & AUX_IRQ_STATUS_AUX_RPLY_TOUT) {
+		/*
+		 * The hardware tried the message seven times per the DP spec
+		 * but it hit a timeout. We ignore defers here because they're
+		 * handled in hardware.
+		 */
+		return -ETIMEDOUT;
+	}
+	if (val & AUX_IRQ_STATUS_AUX_SHORT) {
+		ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &len);
+		if (ret)
+			return ret;
+	} else if (val & AUX_IRQ_STATUS_NAT_I2C_FAIL) {
+		switch (request) {
+		case DP_AUX_I2C_WRITE:
+		case DP_AUX_I2C_READ:
+			msg->reply |= DP_AUX_I2C_REPLY_NACK;
+			break;
+		case DP_AUX_NATIVE_READ:
+		case DP_AUX_NATIVE_WRITE:
+			msg->reply |= DP_AUX_NATIVE_REPLY_NACK;
+			break;
+		}
+		return 0;
+	}
 
 	if (request == DP_AUX_NATIVE_WRITE || request == DP_AUX_I2C_WRITE ||
 	    len == 0)
-- 
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