Re: [PATCH 2/7] drm/i915: Work around DISPLAY_PHY_CONTROL register corruption on CHV

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, May 08, 2015 at 06:24:42PM +0530, Deepak S wrote:
> 
> 
> On Friday 10 April 2015 08:51 PM, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Sometimes (exactly when is a bit unclear) DISPLAY_PHY_CONTROL appears to
> > get corrupted. The values I've managed to read from it seem to have some
> > pattern but vary quite a lot. The corruption doesn't seem to just happen
> > when the register is accessed, but can also happen spontaneosly during
> > modeset. When this happens during a modeset things go south and the
> > display doesn't light up.
> >
> > I've managed to hit the problemn when toggling HDMI on port D on and
> > off. When things get corrupted the display doesn't light up, but as soon
> > as I manually write the correct value to the register the display comes
> > up.
> >
> > First I was suspicious that we ourselves accidentally overwrite it with
> > garbage, but didn't catch anything with the reg_rw tracepoint. Also I
> > sprinkled check all over the modeset path to see exactly when the
> > corruption happens, and eg. the read back value was fine just before
> > intel_dp_set_m(), and corrupted immediately after it. I also made my
> > check function repair the register value whenever it was wrong, and with
> > this approach the corruption repeated several times during the modeset
> > operation, always seeming to trigger in the same exact calls to the
> > check function, while other calls to the function never caught anything.
> >
> > So far I've not seen this problem occurring when carefully avoiding all
> > read accesses to DISPLAY_PHY_CONTROL. Not sure if that's just pure luck
> > or an actual workaround, but we can hope it works. So let's avoid reading
> > the register and instead track the desired value of the register in dev_priv.
> >
> > v2: Read out the power well state to determine initial register value
> > v3: Use DPIO_CHx names instead of raw numbers
> 
> Even reading once DISPLAY_PHY_CONTROL layer is getting corrupted?

Not always. I think it somehow depends on what other register accesses
happen around it. So there is perhaps some magic sequence that might allow
reading it, but I decided that it's better to be safe and never read it.

> I saw similar issues on my setup. On some platform access phy is causing system behave inconsistently  :(
> 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_drv.h         |  2 ++
> >   drivers/gpu/drm/i915/i915_reg.h         |  5 ++++-
> >   drivers/gpu/drm/i915/intel_runtime_pm.c | 36 ++++++++++++++++++++++++++++-----
> >   3 files changed, 37 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 822f259..288c3fc 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -1754,6 +1754,8 @@ struct drm_i915_private {
> >   
> >   	u32 fdi_rx_config;
> >   
> > +	u32 chv_phy_control;
> > +
> >   	u32 suspend_count;
> >   	struct i915_suspend_saved_registers regfile;
> >   	struct vlv_s0ix_state vlv_s0ix_state;
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index cfbd5a6..98588d5 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -1887,7 +1887,10 @@ enum skl_disp_power_wells {
> >   #define DPIO_PHY_STATUS			(VLV_DISPLAY_BASE + 0x6240)
> >   #define   DPLL_PORTD_READY_MASK		(0xf)
> >   #define DISPLAY_PHY_CONTROL (VLV_DISPLAY_BASE + 0x60100)
> > -#define   PHY_COM_LANE_RESET_DEASSERT(phy) (1 << (phy))
> > +#define   PHY_CH_SU_PSR				0x1
> > +#define   PHY_CH_DEEP_PSR			0x7
> 
> PHY_CH_DEEP_PSR defined but not used in this patch?

Just wanted to define it since it's the only other valid value, and the
doc situation is crap. I've not played around with PSR so I'm not
entirely sure how these would be used in practise. My gut is telling me
SU_PSR might be used with link standby and DEEP_PSR with link off, but
that's just a hunch at this point.

You'll see in later patches that we'll start using the override bits to
force the power state, so I think at that point these don't even matter.
But I suppose when we enter PSR we should drop the override bits to
allow the hardware to manage the power states based on the PSR mode
selected.

> 
> other than this, patch does what it says.
> Reviewed-by:  Deepak S<deepak.s@linux.intel.com>
> 
> > +#define   PHY_CH_POWER_MODE(mode, phy, ch)	((mode) << (6*(phy)+3*(ch)+2))
> > +#define   PHY_COM_LANE_RESET_DEASSERT(phy)	(1 << (phy))
> >   #define DISPLAY_PHY_STATUS (VLV_DISPLAY_BASE + 0x60104)
> >   #define   PHY_POWERGOOD(phy)	(((phy) == DPIO_PHY0) ? (1<<31) : (1<<30))
> >   
> > diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > index ce00e69..b73671f 100644
> > --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > @@ -666,8 +666,8 @@ static void chv_dpio_cmn_power_well_enable(struct drm_i915_private *dev_priv,
> >   	if (wait_for(I915_READ(DISPLAY_PHY_STATUS) & PHY_POWERGOOD(phy), 1))
> >   		DRM_ERROR("Display PHY %d is not power up\n", phy);
> >   
> > -	I915_WRITE(DISPLAY_PHY_CONTROL, I915_READ(DISPLAY_PHY_CONTROL) |
> > -		   PHY_COM_LANE_RESET_DEASSERT(phy));
> > +	dev_priv->chv_phy_control |= PHY_COM_LANE_RESET_DEASSERT(phy);
> > +	I915_WRITE(DISPLAY_PHY_CONTROL, dev_priv->chv_phy_control);
> >   }
> >   
> >   static void chv_dpio_cmn_power_well_disable(struct drm_i915_private *dev_priv,
> > @@ -687,8 +687,8 @@ static void chv_dpio_cmn_power_well_disable(struct drm_i915_private *dev_priv,
> >   		assert_pll_disabled(dev_priv, PIPE_C);
> >   	}
> >   
> > -	I915_WRITE(DISPLAY_PHY_CONTROL, I915_READ(DISPLAY_PHY_CONTROL) &
> > -		   ~PHY_COM_LANE_RESET_DEASSERT(phy));
> > +	dev_priv->chv_phy_control &= ~PHY_COM_LANE_RESET_DEASSERT(phy);
> > +	I915_WRITE(DISPLAY_PHY_CONTROL, dev_priv->chv_phy_control);
> >   
> >   	vlv_set_power_well(dev_priv, power_well, false);
> >   }
> > @@ -1401,6 +1401,30 @@ static void intel_power_domains_resume(struct drm_i915_private *dev_priv)
> >   	mutex_unlock(&power_domains->lock);
> >   }
> >   
> > +static void chv_phy_control_init(struct drm_i915_private *dev_priv)
> > +{
> > +	struct i915_power_well *cmn_bc =
> > +		lookup_power_well(dev_priv, PUNIT_POWER_WELL_DPIO_CMN_BC);
> > +	struct i915_power_well *cmn_d =
> > +		lookup_power_well(dev_priv, PUNIT_POWER_WELL_DPIO_CMN_D);
> > +
> > +	/*
> > +	 * DISPLAY_PHY_CONTROL can get corrupted if read. As a
> > +	 * workaround never ever read DISPLAY_PHY_CONTROL, and
> > +	 * instead maintain a shadow copy ourselves. Use the actual
> > +	 * power well state to reconstruct the expected initial
> > +	 * value.
> > +	 */
> > +	dev_priv->chv_phy_control =
> > +		PHY_CH_POWER_MODE(PHY_CH_SU_PSR, DPIO_PHY0, DPIO_CH0) |
> > +		PHY_CH_POWER_MODE(PHY_CH_SU_PSR, DPIO_PHY0, DPIO_CH1) |
> > +		PHY_CH_POWER_MODE(PHY_CH_SU_PSR, DPIO_PHY1, DPIO_CH0);
> > +	if (cmn_bc->ops->is_enabled(dev_priv, cmn_bc))
> > +		dev_priv->chv_phy_control |= PHY_COM_LANE_RESET_DEASSERT(DPIO_PHY0);
> > +	if (cmn_d->ops->is_enabled(dev_priv, cmn_d))
> > +		dev_priv->chv_phy_control |= PHY_COM_LANE_RESET_DEASSERT(DPIO_PHY1);
> > +}
> > +
> >   static void vlv_cmnlane_wa(struct drm_i915_private *dev_priv)
> >   {
> >   	struct i915_power_well *cmn =
> > @@ -1443,7 +1467,9 @@ void intel_power_domains_init_hw(struct drm_i915_private *dev_priv)
> >   
> >   	power_domains->initializing = true;
> >   
> > -	if (IS_VALLEYVIEW(dev) && !IS_CHERRYVIEW(dev)) {
> > +	if (IS_CHERRYVIEW(dev)) {
> > +		chv_phy_control_init(dev_priv);
> > +	} else if (IS_VALLEYVIEW(dev)) {
> >   		mutex_lock(&power_domains->lock);
> >   		vlv_cmnlane_wa(dev_priv);
> >   		mutex_unlock(&power_domains->lock);
> 
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-- 
Ville Syrjälä
Intel OTC
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