[PATCH v2] drm/i915/dp_mst: Work around Thunderbolt sink disconnect after SINK_COUNT_ESI read

[Imre Deak]

On Mon, May 19, 2025 at 04:53:08PM +0300, Jani Nikula wrote:
> On Mon, 19 May 2025, Imre Deak <imre.deak at intel.com> wrote:
> > Due to a problem in the iTBT DP-in adapter's firmware the sink on a TBT
> > link may get disconnected inadvertently if the SINK_COUNT_ESI and the
> > DP_LINK_SERVICE_IRQ_VECTOR_ESI0 registers are read in a single AUX
> > transaction. Work around the issue by reading these registers in
> > separate transactions.
> >
> > The issue affects MTL+ platforms and will be fixed in the DP-in adapter
> > firmware, however releasing that firmware fix may take some time and is
> > not guaranteed to be available for all systems. Based on this apply the
> > workaround on affected platforms.
> >
> > See HSD #13013007775.
> >
> > v2: Cc'ing Mika Westerberg.
> 
> In general, please don't resend just for the sake of adding a Cc. It
> triggers a full CI rerun.

In this case I wanted that as well.

> BR,
> Jani.
> 
> >
> > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13760
> > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14147
> > Cc: Mika Westerberg <mika.westerberg at linux.intel.com>
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 21297bc4cc00d..208a953b04a2f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4538,6 +4538,23 @@ intel_dp_mst_disconnect(struct intel_dp *intel_dp)
> >  static bool
> >  intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *esi)
> >  {
> > +	struct intel_display *display = to_intel_display(intel_dp);
> > +
> > +	/*
> > +	 * Display WA for HSD #13013007775: mtl/arl/lnl
> > +	 * Read the sink count and link service IRQ registers in separate
> > +	 * transactions to prevent disconnecting the sink on a TBT link
> > +	 * inadvertently.
> > +	 */
> > +	if (IS_DISPLAY_VER(display, 14, 20) && !display->platform.battlemage) {
> > +		if (drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI, esi, 3) != 3)
> > +			return false;
> > +
> > +		/* DP_SINK_COUNT_ESI + 3 == DP_LINK_SERVICE_IRQ_VECTOR_ESI0 */
> > +		return drm_dp_dpcd_readb(&intel_dp->aux, DP_LINK_SERVICE_IRQ_VECTOR_ESI0,
> > +					 &esi[3]) == 1;
> > +	}
> > +
> >  	return drm_dp_dpcd_read(&intel_dp->aux, DP_SINK_COUNT_ESI, esi, 4) == 4;
> >  }
> 
> -- 
> Jani Nikula, Intel