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).
Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_irq.c | 53 +++++++++++++++++++++++++++++++--------
1 file changed, 42 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 156a1a4..a3e41d3 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -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 +682,26 @@ 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 +710,7 @@ 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 +719,7 @@ 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 +727,14 @@ 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;
/*
--
1.7.10.4
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