Commit bee447e2 authored by Matthias Kaehlcke's avatar Matthias Kaehlcke Committed by Neil Armstrong

drm/bridge: dw-hdmi: Refuse DDC/CI transfers on the internal I2C controller

The DDC/CI protocol involves sending a multi-byte request to the
display via I2C, which is typically followed by a multi-byte
response. The internal I2C controller only allows single byte
reads/writes or reads of 8 sequential bytes, hence DDC/CI is not
supported when the internal I2C controller is used. The I2C
transfers complete without errors, however the data in the response
is garbage. Abort transfers to/from slave address 0x37 (DDC) with
-EOPNOTSUPP, to make it evident that the communication is failing.
Signed-off-by: default avatarMatthias Kaehlcke <mka@chromium.org>
Reviewed-by: default avatarDouglas Anderson <dianders@chromium.org>
Reviewed-by: default avatarSean Paul <sean@poorly.run>
Acked-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191002124354.v2.1.I709dfec496f5f0b44a7b61dcd4937924da8d8382@changeid
parent 4340ec45
......@@ -37,6 +37,7 @@
#include "dw-hdmi-cec.h"
#include "dw-hdmi.h"
#define DDC_CI_ADDR 0x37
#define DDC_SEGMENT_ADDR 0x30
#define HDMI_EDID_LEN 512
......@@ -399,6 +400,15 @@ static int dw_hdmi_i2c_xfer(struct i2c_adapter *adap,
u8 addr = msgs[0].addr;
int i, ret = 0;
if (addr == DDC_CI_ADDR)
/*
* The internal I2C controller does not support the multi-byte
* read and write operations needed for DDC/CI.
* TOFIX: Blacklist the DDC/CI address until we filter out
* unsupported I2C operations.
*/
return -EOPNOTSUPP;
dev_dbg(hdmi->dev, "xfer: num: %d, addr: %#x\n", num, addr);
for (i = 0; i < num; i++) {
......
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