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    SubjectRe: [PATCH v2] drm/i915: Keep AUX block running when disabling DPMS for MST
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    On 04/02/2018 02:26 PM, Lyude Paul wrote:
    > While enabling/disabling DPMS before link training with MST hubs is
    > perfectly valid; unfortunately disabling DPMS results in some devices
    > disabling their AUX CH block as well. For SST this isn't as much of a
    > problem, but for MST we need to be able to continue handling aux
    > transactions even when none of the sinks are turned on since it's
    > possible for us to have a single atomic commit which results in
    > disabling each downstream sink, followed by subsequently re-enabling
    > each sink.
    >
    > If we don't do this, we'll end up stalling any pending ESI interrupts
    > from the sink for up to 1ms. Unfortunately, dropping ESIs during this
    > timespan makes it so that link fallback retraining for MST (which I will
    > be submitting to the ML shortly) fails due to the channel EQ failure
    > interrupts potentially getting dropped. Additionally, when performing a
    > modeset that brings the hub status's link status from bad -> good having
    > ESIs disabled for that long causes us to miss the hub's response to us
    > trying to start link training as well.
    >
    > Since any sink with MST is going to support DisplayPort 1.2 anyway, save
    > us the hassle of trying to wait until the sink comes back up and just
    > never shut the aux block down.
    >
    > Changes since v2:
    > - Fix patch name, no functional changes
    >
    > Signed-off-by: Lyude Paul <lyude@redhat.com>
    > Cc: Laura Abbott <labbott@redhat.com>
    > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
    > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    > Cc: stable@vger.kernel.org
    > Fixes: ad260ab32a4d9 ("drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.")

    Still able to boot docked and lid closed so

    Tested-by: Laura Abbott <labbott@redhat.com>

    > ---
    > drivers/gpu/drm/i915/intel_dp.c | 6 ++++--
    > 1 file changed, 4 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
    > index 62f82c4298ac..0479c377981b 100644
    > --- a/drivers/gpu/drm/i915/intel_dp.c
    > +++ b/drivers/gpu/drm/i915/intel_dp.c
    > @@ -2589,11 +2589,13 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
    > return;
    >
    > if (mode != DRM_MODE_DPMS_ON) {
    > + unsigned char data = intel_dp->is_mst ?
    > + DP_SET_POWER_D3_AUX_ON : DP_SET_POWER_D3;
    > +
    > if (downstream_hpd_needs_d0(intel_dp))
    > return;
    >
    > - ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
    > - DP_SET_POWER_D3);
    > + ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER, data);
    > } else {
    > struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
    >
    >

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