Tighten the timestamp queries before/after the register read so that we
have less uncertainity for when the read actually took place. This is
more apt for the older generations where it is not a simple single
register read. Whether we are able to discern an improvement in our
sampling accuracy remains to be seen.
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
---
drivers/gpu/drm/i915/i915_irq.c | 57 ++++++++++++++++++++++++---------
1 file changed, 42 insertions(+), 15 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 8e823ba25f5f..9c44df8ecce7 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -713,7 +713,9 @@ u32 g4x_get_vblank_counter(struct drm_crtc *crtc)
* This function will use Framestamp and current
* timestamp registers to calculate the scanline.
*/
-static u32 __intel_get_crtc_scanline_from_timestamp(struct intel_crtc *crtc)
+static u32
+__intel_get_crtc_scanline_from_timestamp(struct intel_crtc *crtc,
+ ktime_t *stime, ktime_t *etime)
{
struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
struct drm_vblank_crtc *vblank =
@@ -737,6 +739,9 @@ static u32 __intel_get_crtc_scanline_from_timestamp(struct
intel_crtc *crtc)
* pipe frame time stamp. The time stamp value
* is sampled at every start of vertical blank.
*/
+ if (stime)
+ *stime = ktime_get();
+
scan_prev_time = intel_de_read_fw(dev_priv,
PIPE_FRMTMSTMP(crtc->pipe));
@@ -746,6 +751,9 @@ static u32 __intel_get_crtc_scanline_from_timestamp(struct
intel_crtc *crtc)
*/
scan_curr_time = intel_de_read_fw(dev_priv, IVB_TIMESTAMP_CTR);
+ if (etime)
+ *etime = ktime_get();
+
scan_post_time = intel_de_read_fw(dev_priv,
PIPE_FRMTMSTMP(crtc->pipe));
} while (scan_post_time != scan_prev_time);
@@ -762,7 +770,8 @@ static u32 __intel_get_crtc_scanline_from_timestamp(struct
intel_crtc *crtc)
* intel_de_read_fw(), only for fast reads of display block, no need for
* forcewake etc.
*/
-static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
+static int __intel_get_crtc_scanline(struct intel_crtc *crtc,
+ ktime_t *stime, ktime_t *etime)
{
struct drm_device *dev = crtc->base.dev;
struct drm_i915_private *dev_priv = to_i915(dev);
@@ -771,23 +780,34 @@ static int __intel_get_crtc_scanline(struct intel_crtc
*crtc)
enum pipe pipe = crtc->pipe;
int position, vtotal;
- if (!crtc->active)
+ if (!crtc->active) {
+ if (stime)
+ *stime = 0;
+ if (etime)
+ *etime = 0;
return -1;
+ }
vblank = &crtc->base.dev->vblank[drm_crtc_index(&crtc->base)];
mode = &vblank->hwmode;
if (crtc->mode_flags & I915_MODE_FLAG_GET_SCANLINE_FROM_TIMESTAMP)
- return __intel_get_crtc_scanline_from_timestamp(crtc);
+ return __intel_get_crtc_scanline_from_timestamp(crtc,
+ stime,
+ etime);
vtotal = mode->crtc_vtotal;
if (mode->flags & DRM_MODE_FLAG_INTERLACE)
vtotal /= 2;
+ if (stime)
+ *stime = ktime_get();
if (IS_GEN(dev_priv, 2))
position = intel_de_read_fw(dev_priv, PIPEDSL(pipe)) &
DSL_LINEMASK_GEN2;
else
position = intel_de_read_fw(dev_priv, PIPEDSL(pipe)) &
DSL_LINEMASK_GEN3;
+ if (etime)
+ *etime = ktime_get();
/*
* On HSW, the DSL reg (0x70000) appears to return 0 if we
@@ -806,7 +826,13 @@ static int __intel_get_crtc_scanline(struct intel_crtc
*crtc)
for (i = 0; i < 100; i++) {
udelay(1);
+
+ if (stime)
+ *stime = ktime_get();
temp = intel_de_read_fw(dev_priv, PIPEDSL(pipe)) &
DSL_LINEMASK_GEN3;
+ if (etime)
+ *etime = ktime_get();
+
if (temp != position) {
position = temp;
break;
@@ -866,21 +892,25 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc
*_crtc,
/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
- /* Get optional system timestamp before query. */
- if (stime)
- *stime = ktime_get();
-
if (use_scanline_counter) {
/* No obvious pixelcount register. Only query vertical
* scanout position from Display scan line register.
*/
- position = __intel_get_crtc_scanline(crtc);
+ position = __intel_get_crtc_scanline(crtc, stime, etime);
} else {
+ /* Get optional system timestamp before query. */
+ if (stime)
+ *stime = ktime_get();
+
/* Have access to pixelcount since start of frame.
* We can split this into vertical and horizontal
* scanout position.
*/
- position = (intel_de_read_fw(dev_priv, PIPEFRAMEPIXEL(pipe)) &
PIPE_PIXEL_MASK) >> PIPE_PIXEL_SHIFT;
+ position = intel_de_read_fw(dev_priv, PIPEFRAMEPIXEL(pipe));
+
+ /* Get optional system timestamp after query. */
+ if (etime)
+ *etime = ktime_get();
/* convert to pixel counts */
vbl_start *= htotal;
@@ -896,6 +926,7 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
* matches how the scanline counter based position works since
* the scanline counter doesn't count the two half lines.
*/
+ position = (position & PIPE_PIXEL_MASK) >> PIPE_PIXEL_SHIFT;
if (position >= vtotal)
position = vtotal - 1;
@@ -911,10 +942,6 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc
*_crtc,
position = (position + htotal - hsync_start) % vtotal;
}
- /* 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);
@@ -956,7 +983,7 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc)
int position;
spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
- position = __intel_get_crtc_scanline(crtc);
+ position = __intel_get_crtc_scanline(crtc, NULL, NULL);
spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
return position;
--
2.27.0
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