linux-kernel - [PATCH v3] drm/bridge: it6505: fix HDCP V match check is not performed correctly

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Message-Id: <20250109-fix-hdcp-v-comp-v3-1-1258edb249ab@ite.com.tw>
Date: Thu, 09 Jan 2025 14:40:08 +0800
From: Hermes Wu via B4 Relay <devnull+Hermes.wu.ite.com.tw@...nel.org>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
 Hermes Wu <hermes.wu@....com.tw>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Pet.Weng@....com.tw, Kenneth.Hung@....com.tw, treapking@...omium.org, 
 Hermes Wu <Hermes.wu@....com.tw>
Subject: [PATCH v3] drm/bridge: it6505: fix HDCP V match check is not
 performed correctly

From: Hermes Wu <Hermes.wu@....com.tw>

The loop of V compare is expected to iterate for 5 times
which compare V array form av[0][] to av[4][].
It should check loop counter reach the last statement "i == 5"
before return true

Fixes: 0989c02c7a5c ("drm/bridge: it6505: fix HDCP CTS compare V matching")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
---
Changes in v3:
- The V value compare loop from i = 0 to i = 4 and shall exit with i == 5 
  if all V element matches
- Link to v2: https://lore.kernel.org/r/20250109-fix-hdcp-v-comp-v2-1-7dce0a59523f@ite.com.tw

Changes in v2:
- pull the check of statment "i" out of V value check loop 
- Link to v1: https://lore.kernel.org/r/20250108-fix-hdcp-v-comp-v1-1-9404811825cd@ite.com.tw
---
 drivers/gpu/drm/bridge/ite-it6505.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
index 88ef76a37fe6accacdd343839ff2569b31b18ceb..2f82fbc0b8bf8c322c088dc257720c6825651bb8 100644
--- a/drivers/gpu/drm/bridge/ite-it6505.c
+++ b/drivers/gpu/drm/bridge/ite-it6505.c
@@ -2250,12 +2250,13 @@ static bool it6505_hdcp_part2_ksvlist_check(struct it6505 *it6505)
 			continue;
 		}
 
-		for (i = 0; i < 5; i++) {
+		for (i = 0; i < 5; i++)
 			if (bv[i][3] != av[i][0] || bv[i][2] != av[i][1] ||
 			    av[i][1] != av[i][2] || bv[i][0] != av[i][3])
 				break;
 
-			DRM_DEV_DEBUG_DRIVER(dev, "V' all match!! %d, %d", retry, i);
+		if (i == 5) {
+			DRM_DEV_DEBUG_DRIVER(dev, "V' all match!! %d", retry);
 			return true;
 		}
 	}

---
base-commit: 938fbb16aba8f7b88e0fdcf56f315a5bbad41aad
change-id: 20250107-fix-hdcp-v-comp-3ba8e3d7adf3

Best regards,
-- 
Hermes Wu <Hermes.wu@....com.tw>