Re: [PATCH v2 1/3] drm/i915: Skip register reads in i915_get_crtc_scanoutpos()

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

On Wed, Sep 25, 2013 at 04:35:56AM +0200, Mario Kleiner wrote:
> On 23.09.13 13:48, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > We have all the information we need in the mode structure, so going and
> > reading it from the hardware is pointless, and slower.
> >
> > We never populated ->get_vblank_timestamp() in the UMS case, and as that
> > is the only way we'd ever call ->get_scanout_position(), we can
> > completely ignore UMS in i915_get_crtc_scanoutpos().
> >
> > Also reorganize intel_irq_init() a bit to clarify the KMS vs. UMS
> > situation.
> >
> > v2: Drop UMS code
> >
> > Cc: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_irq.c | 43 ++++++++++++++++-------------------------
> >   1 file changed, 17 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index b356dc1..058f099 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -570,24 +570,29 @@ static u32 gm45_get_vblank_counter(struct drm_device *dev, int pipe)
> >   static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,
> >   			     int *vpos, int *hpos)
> >   {
> > -	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
> > -	u32 vbl = 0, position = 0;
> > +	struct drm_i915_private *dev_priv = dev->dev_private;
> > +	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
> > +	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> > +	const struct drm_display_mode *mode = &intel_crtc->config.adjusted_mode;
> > +	u32 position;
> >   	int vbl_start, vbl_end, htotal, vtotal;
> >   	bool in_vbl = true;
> >   	int ret = 0;
> > -	enum transcoder cpu_transcoder = intel_pipe_to_cpu_transcoder(dev_priv,
> > -								      pipe);
> >
> > -	if (!i915_pipe_enabled(dev, pipe)) {
> > +	if (!intel_crtc->active) {
> >   		DRM_DEBUG_DRIVER("trying to get scanoutpos for disabled "
> >   				 "pipe %c\n", pipe_name(pipe));
> >   		return 0;
> >   	}
> >
> > -	/* Get vtotal. */
> > -	vtotal = 1 + ((I915_READ(VTOTAL(cpu_transcoder)) >> 16) & 0x1fff);
> > +	htotal = mode->crtc_htotal;
> > +	vtotal = mode->crtc_vtotal;
> > +	vbl_start = mode->crtc_vblank_start;
> > +	vbl_end = mode->crtc_vblank_end;
> >
> > -	if (INTEL_INFO(dev)->gen >= 4) {
> > +	ret |= DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE;
> > +
> > +	if (IS_G4X(dev) || INTEL_INFO(dev)->gen >= 5) {
> >   		/* No obvious pixelcount register. Only query vertical
> >   		 * scanout position from Display scan line register.
> >   		 */
> > @@ -605,29 +610,16 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,
> >   		 */
> >   		position = (I915_READ(PIPEFRAMEPIXEL(pipe)) & PIPE_PIXEL_MASK) >> PIPE_PIXEL_SHIFT;
> >
> > -		htotal = 1 + ((I915_READ(HTOTAL(cpu_transcoder)) >> 16) & 0x1fff);
> >   		*vpos = position / htotal;
> >   		*hpos = position - (*vpos * htotal);
> >   	}
> >
> > -	/* Query vblank area. */
> > -	vbl = I915_READ(VBLANK(cpu_transcoder));
> > -
> > -	/* Test position against vblank region. */
> > -	vbl_start = vbl & 0x1fff;
> > -	vbl_end = (vbl >> 16) & 0x1fff;
> > -
> > -	if ((*vpos < vbl_start) || (*vpos > vbl_end))
> > -		in_vbl = false;
> > +	in_vbl = *vpos >= vbl_start && *vpos < vbl_end;
> 
> I think this should be a <= instead of < in *vpos < vbl_end, if it is 
> meant to be equal to the line it replaces (not >  is <=), unless the 
> original comparison was off-by-one?

Yeah, I think the original was wrong, in more ways than one. It forgot
to add +1 to vbl_start/end, and then it did the comparison wrong as
well.

> 
>  > +	in_vbl = *vpos >= vbl_start && *vpos <= vbl_end;
> 
> Other than that, it looks good.
> 
> Reviewed-by: mario.kleiner.de@gmail.com
> 
> >
> >   	/* Inside "upper part" of vblank area? Apply corrective offset: */
> >   	if (in_vbl && (*vpos >= vbl_start))
> >   		*vpos = *vpos - vtotal;
> >
> > -	/* Readouts valid? */
> > -	if (vbl > 0)
> > -		ret |= DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE;
> > -
> >   	/* In vblank? */
> >   	if (in_vbl)
> >   		ret |= DRM_SCANOUTPOS_INVBL;
> > @@ -3148,11 +3140,10 @@ void intel_irq_init(struct drm_device *dev)
> >   		dev->driver->get_vblank_counter = gm45_get_vblank_counter;
> >   	}
> >
> > -	if (drm_core_check_feature(dev, DRIVER_MODESET))
> > +	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
> >   		dev->driver->get_vblank_timestamp = i915_get_vblank_timestamp;
> > -	else
> > -		dev->driver->get_vblank_timestamp = NULL;
> > -	dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
> > +		dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
> > +	}
> >
> >   	if (IS_VALLEYVIEW(dev)) {
> >   		dev->driver->irq_handler = valleyview_irq_handler;
> >

-- 
Ville Syrjälä
Intel OTC