linux-kernel - [PATCH v2 08/15] drm/bridge: tc358767: Increase AUX transfer length limit

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Message-Id: <20190322032901.12045-9-andrew.smirnov@gmail.com>
Date:   Thu, 21 Mar 2019 20:28:54 -0700
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Andrey Smirnov <andrew.smirnov@...il.com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Andrey Gusakov <andrey.gusakov@...entembedded.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 08/15] drm/bridge: tc358767: Increase AUX transfer length limit

According to the datasheet tc358767 can transfer up to 16 bytes via
its AUX channel, so the artificial limit of 8 apperas to be too
low. However only up to 15-bytes seem to be actually supported and
trying to use 16-byte transfers results in transfers failing
sporadically (with bogus status in case of I2C transfers), so limit it
to 15.

Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
Cc: Archit Taneja <architt@...eaurora.org>
Cc: Andrzej Hajda <a.hajda@...sung.com>
Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Cc: Tomi Valkeinen <tomi.valkeinen@...com>
Cc: Andrey Gusakov <andrey.gusakov@...entembedded.com>
Cc: Philipp Zabel <p.zabel@...gutronix.de>
Cc: Chris Healy <cphealy@...il.com>
Cc: Lucas Stach <l.stach@...gutronix.de>
Cc: dri-devel@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org
---
 drivers/gpu/drm/bridge/tc358767.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
index 21374565585d..8adaac5ca271 100644
--- a/drivers/gpu/drm/bridge/tc358767.c
+++ b/drivers/gpu/drm/bridge/tc358767.c
@@ -358,7 +358,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 			       struct drm_dp_aux_msg *msg)
 {
 	struct tc_data *tc = aux_to_tc(aux);
-	size_t size = min_t(size_t, 8, msg->size);
+	size_t size = min_t(size_t, DP_AUX_MAX_PAYLOAD_BYTES - 1, msg->size);
 	u8 request = msg->request & ~DP_AUX_I2C_MOT;
 	int ret;
 
-- 
2.20.1