From: Matthias Kaehlcke <mka@xxxxxxxxxxxx> [ Upstream commit bee447e224b2645911c5d06e35dc90d8433fcef6 ] 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: Matthias Kaehlcke <mka@xxxxxxxxxxxx> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Reviewed-by: Sean Paul <sean@xxxxxxxxxx> Acked-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx> Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20191002124354.v2.1.I709dfec496f5f0b44a7b61dcd4937924da8d8382@changeid Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index 5971976284bf..fb396d550275 100644 --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c @@ -39,6 +39,7 @@ #include <media/cec-notifier.h> +#define DDC_CI_ADDR 0x37 #define DDC_SEGMENT_ADDR 0x30 #define HDMI_EDID_LEN 512 @@ -320,6 +321,15 @@ 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++) { -- 2.20.1
