On Mon, 2018-04-02 at 17:21 -0400, 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.
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.")
We've come a full circle on this one :)
1) Originally, we had disable_ddi() setting the branch power state to D3. 2) Then "Use MST sideband message transactions for dpms control" removed that as a bug fix for some devices. The sideband solution was chosen over the D3_AUX_ON approach this patch takes. 3) Next, "Write to SET_POWER dpcd to enable MST hub" effectively took us back to the original state due to a regression. 4) Now, we are calling (3) a regression and implementing D3_AUX_ON.
I guess, this combination should work for most devices. But, we should test this on a few different MST hubs before going ahead.
-DK
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);