Commit ad3543ed authored by Mario Kleiner's avatar Mario Kleiner Committed by Dave Airlie
Browse files

drm/intel: Push get_scanout_position() timestamping into kms driver. 



Move the ktime_get() clock readouts and potential preempt_disable()
calls from drm core into kms driver to make it compatible with the
api changes in the drm core.

The intel-kms driver needs to take the uncore.lock inside
i915_get_crtc_scanoutpos() and intel_pipe_in_vblank().
This is incompatible with the preempt_disable() on a
PREEMPT_RT patched kernel, as regular spin locks must not
be taken within a preempt_disable'd section. Lock contention
on the uncore.lock also introduced too much uncertainty in vblank
timestamps.

Push the ktime_get() timestamping for scanoutpos queries and
potential preempt_disable_rt() into i915_get_crtc_scanoutpos(),
so these problems can be avoided:

1. First lock the uncore.lock (might sleep on a PREEMPT_RT kernel).
2. preempt_disable_rt() (will be added by the rt-linux folks).
3. ktime_get() a timestamp before scanout pos query.
4. Do all mmio reads as fast as possible without grabbing any new locks!
5. ktime_get() a post-query timestamp.
6. preempt_enable_rt()
7. Unlock the uncore.lock.

This reduces timestamp uncertainty on a low-end HP Atom Mini netbook
with Intel GMA-950 nicely:

Before: 3-8 usecs with spikes > 20 usecs, triggering query retries.
After : Typically 1 usec (98% of all samples), occassionally 2 usecs
        (2% of all samples), with maximum of 3 usecs (a handful).

v2: Fix formatting of new multi-line code comments.

Signed-off-by: default avatarMario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent d47abc58

drivers/gpu/drm/i915/i915_irq.c

+43 −11
Original line number Diff line number Diff line
@@ -599,35 +599,40 @@ static u32 gm45_get_vblank_counter(struct drm_device *dev, int pipe) 
	return I915_READ(reg);

}



static bool intel_pipe_in_vblank(struct drm_device *dev, enum pipe pipe)

/* raw reads, only for fast reads of display block, no need for forcewake etc. */

#define __raw_i915_read32(dev_priv__, reg__) readl((dev_priv__)->regs + (reg__))

#define __raw_i915_read16(dev_priv__, reg__) readw((dev_priv__)->regs + (reg__))



static bool intel_pipe_in_vblank_locked(struct drm_device *dev, enum pipe pipe)

{

	struct drm_i915_private *dev_priv = dev->dev_private;

	uint32_t status;

	int reg;



	if (IS_VALLEYVIEW(dev)) {

		status = pipe == PIPE_A ?

			I915_DISPLAY_PIPE_A_VBLANK_INTERRUPT :

			I915_DISPLAY_PIPE_B_VBLANK_INTERRUPT;



		return I915_READ(VLV_ISR) & status;

		reg = VLV_ISR;

	} else if (IS_GEN2(dev)) {

		status = pipe == PIPE_A ?

			I915_DISPLAY_PIPE_A_VBLANK_INTERRUPT :

			I915_DISPLAY_PIPE_B_VBLANK_INTERRUPT;



		return I915_READ16(ISR) & status;

		reg = ISR;

	} else if (INTEL_INFO(dev)->gen < 5) {

		status = pipe == PIPE_A ?

			I915_DISPLAY_PIPE_A_VBLANK_INTERRUPT :

			I915_DISPLAY_PIPE_B_VBLANK_INTERRUPT;



		return I915_READ(ISR) & status;

		reg = ISR;

	} else if (INTEL_INFO(dev)->gen < 7) {

		status = pipe == PIPE_A ?

			DE_PIPEA_VBLANK :

			DE_PIPEB_VBLANK;



		return I915_READ(DEISR) & status;

		reg = DEISR;

	} else {

		switch (pipe) {

		default:
@@ -642,12 +647,17 @@ static bool intel_pipe_in_vblank(struct drm_device *dev, enum pipe pipe) 
			break;

		}



		return I915_READ(DEISR) & status;

		reg = DEISR;

	}



	if (IS_GEN2(dev))

		return __raw_i915_read16(dev_priv, reg) & status;

	else

		return __raw_i915_read32(dev_priv, reg) & status;

}



static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,

			     int *vpos, int *hpos)

			     int *vpos, int *hpos, ktime_t *stime, ktime_t *etime)

{

	struct drm_i915_private *dev_priv = dev->dev_private;

	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
@@ -657,6 +667,7 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, 
	int vbl_start, vbl_end, htotal, vtotal;

	bool in_vbl = true;

	int ret = 0;

	unsigned long irqflags;



	if (!intel_crtc->active) {

		DRM_DEBUG_DRIVER("trying to get scanoutpos for disabled "
@@ -671,14 +682,27 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, 


	ret |= DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE;



	/*

	 * Lock uncore.lock, as we will do multiple timing critical raw

	 * register reads, potentially with preemption disabled, so the

	 * following code must not block on uncore.lock.

	 */

	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);

	

	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */



	/* Get optional system timestamp before query. */

	if (stime)

		*stime = ktime_get();



	if (IS_GEN2(dev) || IS_G4X(dev) || INTEL_INFO(dev)->gen >= 5) {

		/* No obvious pixelcount register. Only query vertical

		 * scanout position from Display scan line register.

		 */

		if (IS_GEN2(dev))

			position = I915_READ(PIPEDSL(pipe)) & DSL_LINEMASK_GEN2;

			position = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & DSL_LINEMASK_GEN2;

		else

			position = I915_READ(PIPEDSL(pipe)) & DSL_LINEMASK_GEN3;

			position = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & DSL_LINEMASK_GEN3;



		/*

		 * The scanline counter increments at the leading edge
@@ -687,7 +711,7 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, 
		 * to get a more accurate picture whether we're in vblank

		 * or not.

		 */

		in_vbl = intel_pipe_in_vblank(dev, pipe);

		in_vbl = intel_pipe_in_vblank_locked(dev, pipe);

		if ((in_vbl && position == vbl_start - 1) ||

		    (!in_vbl && position == vbl_end - 1))

			position = (position + 1) % vtotal;
@@ -696,7 +720,7 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, 
		 * We can split this into vertical and horizontal

		 * scanout position.

		 */

		position = (I915_READ(PIPEFRAMEPIXEL(pipe)) & PIPE_PIXEL_MASK) >> PIPE_PIXEL_SHIFT;

		position = (__raw_i915_read32(dev_priv, PIPEFRAMEPIXEL(pipe)) & PIPE_PIXEL_MASK) >> PIPE_PIXEL_SHIFT;



		/* convert to pixel counts */

		vbl_start *= htotal;
@@ -704,6 +728,14 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, 
		vtotal *= htotal;

	}



	/* Get optional system timestamp after query. */

	if (etime)

		*etime = ktime_get();



	/* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */



	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);



	in_vbl = position >= vbl_start && position < vbl_end;



	/*

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