[PATCH 4.20 047/352] drm/rockchip: fix for mailbox read size

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit fa68d4f8476bea4cdf441062b614b41bb85ef1da ]

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@xxxxxxxxxxx>
Signed-off-by: Heiko Stuebner <heiko@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/1541518625-25984-1-git-send-email-dkos@xxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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;
-- 
2.19.1