linux-kernel - [PATCH] drm/rockchip: fix for mailbox read size

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Message-ID: <1541518625-25984-1-git-send-email-dkos@cadence.com>
Date:   Tue, 6 Nov 2018 15:37:05 +0000
From:   Damian Kos <dkos@...ence.com>
To:     Chris Zhong <zyw@...k-chips.com>, Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        David Airlie <airlied@...ux.ie>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     Damian Kos <dkos@...ence.com>
Subject: [PATCH] drm/rockchip: fix for mailbox read size

Some of the functions (like cdn_dp_dpcd_read, cdn_dp_get_edid_block)
allow to read 64KiB, but the cdn_dp_mailbox_read_receive, that is
used by them, can read only up to 255 bytes at once. Normally, it's
not a big issue as DPCD or EDID reads won't (hopefully) exceed that
value.
The real issue here is the revocation list read during the HDCP
authentication process. (problematic use case:
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-4.4/drivers/gpu/drm/rockchip/cdn-dp-reg.c#1152)
The list can reach 127*5+4 bytes (num devs * 5 bytes per ID/Bksv +
4 bytes of an additional info).
In other words - CTSes with HDCP Repeater won't pass without this
fix. Oh, and the driver will most likely stop working (best case
scenario).

Signed-off-by: Damian Kos <dkos@...ence.com>
---
 drivers/gpu/drm/rockchip/cdn-dp-reg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/rockchip/cdn-dp-reg.c b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
index 3105965fc260..5a485489a1e2 100644
--- a/drivers/gpu/drm/rockchip/cdn-dp-reg.c
+++ b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
@@ -147,7 +147,7 @@ static int cdn_dp_mailbox_validate_receive(struct cdn_dp_device *dp,
 }

 static int cdn_dp_mailbox_read_receive(struct cdn_dp_device *dp,
-				       u8 *buff, u8 buff_size)
+				       u8 *buff, u16 buff_size)
 {
 	u32 i;
 	int ret;
-- 
2.17.1