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    Subject[PATCH v3 17/43] drm/bridge: analogix_dp: Wait for HPD signal before configuring link
    Date
    From: zain wang <wzz@rock-chips.com>

    According to DP spec v1.3 chap 3.5.1.2 Link Training, Link Policy Maker
    must first detect that the HPD signal is asserted high by the Downstream
    Device before establishing a link with it.

    Cc: Stéphane Marchesin <marcheu@chromium.org>
    Signed-off-by: zain wang <wzz@rock-chips.com>
    Signed-off-by: Sean Paul <seanpaul@chromium.org>
    Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
    ---
    drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
    index ba2506e17f6d..c940a5bb80ac 100644
    --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
    +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
    @@ -1170,6 +1170,17 @@ static int analogix_dp_set_bridge(struct analogix_dp_device *dp)
    if (ret)
    goto out_dp_init;

    + /*
    + * According to DP spec v1.3 chap 3.5.1.2 Link Training,
    + * We should first make sure the HPD signal is asserted high by device
    + * when we want to establish a link with it.
    + */
    + ret = analogix_dp_detect_hpd(dp);
    + if (ret) {
    + DRM_ERROR("failed to get hpd single ret = %d\n", ret);
    + goto out_dp_init;
    + }
    +
    ret = analogix_dp_commit(dp);
    if (ret)
    goto out_dp_init;
    --
    2.14.1
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