From: Matthias Kaehlcke mka@chromium.org
[ 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@chromium.org Reviewed-by: Douglas Anderson dianders@chromium.org Reviewed-by: Sean Paul sean@poorly.run Acked-by: Neil Armstrong narmstrong@baylibre.com Signed-off-by: Neil Armstrong narmstrong@baylibre.com Link: https://patchwork.freedesktop.org/patch/msgid/20191002124354.v2.1.I709dfec49... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 521d689413c8..3e82d604201e 100644 --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c @@ -36,6 +36,7 @@ #include "dw-hdmi-cec.h" #include "dw-hdmi.h"
+#define DDC_CI_ADDR 0x37 #define DDC_SEGMENT_ADDR 0x30
#define HDMI_EDID_LEN 512 @@ -398,6 +399,15 @@ 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++) {