Re: [PATCH 06/10] drm/i915/icl: Mark TC port as safe when interruptions are disabled

["Souza, Jose" <jose.souza@intel.com>]

On Wed, 2018-10-10 at 20:15 +0300, Ville Syrjälä wrote:
> On Wed, Oct 10, 2018 at 12:55:07AM +0000, Souza, Jose wrote:
> > On Tue, 2018-10-02 at 23:35 +0300, Ville Syrjälä wrote:
> > > On Tue, Oct 02, 2018 at 10:50:50AM -0700, José Roberto de Souza
> > > wrote:
> > > > Before enter in power saving states or before unload the driver
> > > > spec states that display driver is required to to mark TC ports
> > > > as
> > > > safe so hardware can do the disconnection flow without wait for
> > > > display driver handshake.
> > > > When driver is resumed or loaded again, if the TC live state is
> > > > still set as connected driver will mark again TC port as not
> > > > safe
> > > > as
> > > > required by spec.
> > > > 
> > > > BSpec: 2175
> > > > 
> > > > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > > > Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/i915_irq.c | 10 ++++++++++
> > > >  1 file changed, 10 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/i915_irq.c
> > > > b/drivers/gpu/drm/i915/i915_irq.c
> > > > index 2e242270e270..58616690f45f 100644
> > > > --- a/drivers/gpu/drm/i915/i915_irq.c
> > > > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > > > @@ -3640,6 +3640,7 @@ static void gen11_irq_reset(struct
> > > > drm_device
> > > > *dev)
> > > >  {
> > > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > > >  	int pipe;
> > > > +	u32 val;
> > > >  
> > > >  	I915_WRITE(GEN11_GFX_MSTR_IRQ, 0);
> > > >  	POSTING_READ(GEN11_GFX_MSTR_IRQ);
> > > > @@ -3661,6 +3662,15 @@ static void gen11_irq_reset(struct
> > > > drm_device *dev)
> > > >  
> > > >  	if (HAS_PCH_ICP(dev_priv))
> > > >  		GEN3_IRQ_RESET(SDE);
> > > > +
> > > > +	/*
> > > > +	 * Mark TC ports as safe so hardware can do the
> > > > disconnect flow
> > > > without
> > > > +	 * wait for driver to do the handshake
> > > > +	 */
> > > > +	val = I915_READ(PORT_TX_DFLEXDPCSSS);
> > > > +	for (pipe = 0; pipe < 4; pipe++)
> > > > +		val &= ~(DP_PHY_MODE_STATUS_NOT_SAFE(pipe));
> > > > +	I915_WRITE(PORT_TX_DFLEXDPCSSS, val);
> > > 
> > > Why would we have to do this here? The driver should relinquish
> > > control
> > > if and when it has shut down the pipes etc. Sounds like a bug if
> > > we're
> > > hanging on when we have no need for the port.
> > 
> > Right now we take control and only release it when port is
> > disconnected.
> 
> Disconnection is totally asynchronous. Someone could be using the
> port/aux for anything when the disconnect irq happens. Presumably
> bad things will happen if we just go and yank the control away
> when someone is doing stuff. I believe even the spec tells us
> to properly shut things down during the disconnect flow and make
> sure eg. the aux power wells have been fully shut down before
> relinquishing control.

In my understanding at the point of the gen11_irq_reset() call all DDI
DDI ports and aux channels are already off.

> 
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