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    Subject[PATCH AUTOSEL 5.4 069/350] drm/bridge: dw-hdmi: Refuse DDC/CI transfers on the internal I2C controller
    Date
    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.I709dfec496f5f0b44a7b61dcd4937924da8d8382@changeid
    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 521d689413c8c..3e82d604201ee 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++) {
    --
    2.20.1
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