Re: [PATCH 2/3] drm/i915: Protect dev_priv->atomic_cdclk_freq with all the crtc locks

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

On Tue, Nov 15, 2016 at 11:14:29AM +0100, Maarten Lankhorst wrote:
> Op 14-11-16 om 17:35 schreef ville.syrjala@linux.intel.com:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > A modeset on one pipe can update dev_priv->atomic_cdclk_freq without
> > actually touching the hardware, in which case we won't force a modeset
> > on all the pipes, and thus won't lock any of the other pipes either.
> > That means a parallel plane update on another pipe could be looking at
> > a stale dev_priv->atomic_cdcdlk_freq and thus fail to notice when the
> > plane configuration is invalid, or potentially reject a valid update.
> >
> > To overcome this we must protect writes to atomic_cdclk_freq with
> > all the crtc locks, and thus for reads any single crtc lock will
> > be sufficient protection.
> >
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h      |  9 +++++++-
> >  drivers/gpu/drm/i915/intel_display.c | 41 +++++++++++++++++++++++++++++++-----
> >  2 files changed, 44 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index c0f1dfc7119e..66d2950dc657 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -1874,7 +1874,14 @@ struct drm_i915_private {
> >  
> >  	unsigned int fsb_freq, mem_freq, is_ddr3;
> >  	unsigned int skl_preferred_vco_freq;
> > -	unsigned int cdclk_freq, max_cdclk_freq, atomic_cdclk_freq;
> > +	unsigned int cdclk_freq, max_cdclk_freq;
> > +
> > +	/*
> > +	 * For reading holding any crtc lock is sufficient,
> > +	 * for writing must hold all of them.
> > +	 */
> > +	unsigned int atomic_cdclk_freq;
> > +
> >  	unsigned int max_dotclk_freq;
> >  	unsigned int rawclk_freq;
> >  	unsigned int hpll_freq;
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 70f3f0b70263..d7a4bc63b05b 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -13946,13 +13946,32 @@ static int haswell_mode_set_planes_workaround(struct drm_atomic_state *state)
> >  	return 0;
> >  }
> >  
> > +static int intel_lock_all_pipes(struct drm_atomic_state *state)
> > +{
> > +	struct drm_crtc *crtc;
> > +
> > +	/* Add all pipes to the state */
> > +	for_each_crtc(state->dev, crtc) {
> > +		struct drm_crtc_state *crtc_state;
> > +
> > +		crtc_state = drm_atomic_get_crtc_state(state, crtc);
> > +		if (IS_ERR(crtc_state))
> > +			return PTR_ERR(crtc_state);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int intel_modeset_all_pipes(struct drm_atomic_state *state)
> >  {
> >  	struct drm_crtc *crtc;
> >  	struct drm_crtc_state *crtc_state;
> >  	int ret = 0;
> >  
> > -	/* add all active pipes to the state */
> > +	/*
> > +	 * Add all pipes to the state, and force
> > +	 * a modeset on all the active ones.
> > +	 */
> >  	for_each_crtc(state->dev, crtc) {
> >  		crtc_state = drm_atomic_get_crtc_state(state, crtc);
> >  		if (IS_ERR(crtc_state))
> > @@ -14018,12 +14037,24 @@ static int intel_modeset_checks(struct drm_atomic_state *state)
> >  		if (ret < 0)
> >  			return ret;
> >  
> > +		/*
> > +		 * Writes to dev_priv->atomic_cdclk_freq must protected by
> > +		 * holding all the crtc locks, even if we don't end up
> > +		 * touching the hardware
> > +		 */
> > +		if (intel_state->cdclk != dev_priv->atomic_cdclk_freq) {
> > +			ret = intel_lock_all_pipes(state);
> > +			if (ret < 0)
> > +				return ret;
> > +		}
> > +
> Would it be terrible to just use intel_modeset_all_pipes here? Since this can only be different in the all crtc's disabled case
> it won't matter much.

Is there any benefit in doing that? A bit confusing IMO to force a
modeset when you don't have to.

-- 
Ville Syrjälä
Intel OTC
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