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    Subject[PATCH 4.2.y-ckt 09/53] drm/radeon: fix DP link training issue with second 4K monitor
    Date
    4.2.8-ckt11 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Arindam Nath <arindam.nath@amd.com>

    commit 1a738347df2ee4977459a8776fe2c62196bdcb1b upstream.

    There is an issue observed when we hotplug a second DP
    4K monitor to the system. Sometimes, the link training
    fails for the second monitor after HPD interrupt
    generation.

    The issue happens when some queued or deferred transactions
    are already present on the AUX channel when we initiate
    a new transcation to (say) get DPCD or during link training.

    We set AUX_IGNORE_HPD_DISCON bit in the AUX_CONTROL
    register so that we can ignore any such deferred
    transactions when a new AUX transaction is initiated.

    Signed-off-by: Arindam Nath <arindam.nath@amd.com>
    Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/gpu/drm/radeon/radeon_dp_auxch.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/gpu/drm/radeon/radeon_dp_auxch.c b/drivers/gpu/drm/radeon/radeon_dp_auxch.c
    index 3b0c229..db64e00 100644
    --- a/drivers/gpu/drm/radeon/radeon_dp_auxch.c
    +++ b/drivers/gpu/drm/radeon/radeon_dp_auxch.c
    @@ -105,7 +105,7 @@ radeon_dp_aux_transfer_native(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg

    tmp &= AUX_HPD_SEL(0x7);
    tmp |= AUX_HPD_SEL(chan->rec.hpd);
    - tmp |= AUX_EN | AUX_LS_READ_EN;
    + tmp |= AUX_EN | AUX_LS_READ_EN | AUX_HPD_DISCON(0x1);

    WREG32(AUX_CONTROL + aux_offset[instance], tmp);

    --
    2.7.4
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