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Subject[PATCH AUTOSEL 4.19 059/167] drm/vblank: Allow dynamic per-crtc max_vblank_count
Date
From: Ville Syrjälä <ville.syrjala@linux.intel.com>

[ Upstream commit ed20151a7699bb2c77eba3610199789a126940c4 ]

On i965gm we need to adjust max_vblank_count dynamically
depending on whether the TV encoder is used or not. To
that end add a per-crtc max_vblank_count that takes
precedence over its device wide counterpart. The driver
can now call drm_crtc_set_max_vblank_count() to configure
the per-crtc value before calling drm_vblank_on().

Also looks like there was some discussion about exynos needing
similar treatment.

v2: Drop the extra max_vblank_count!=0 check for the
WARN(last!=current), will take care of it in i915 code (Daniel)
WARN_ON(!inmodeset) (Daniel)
WARN_ON(dev->max_vblank_count)
Pimp up the docs (Daniel)

Cc: stable@vger.kernel.org
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127182004.28885-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/drm_vblank.c | 45 +++++++++++++++++++++++++++++++++---
include/drm/drm_device.h | 8 ++++++-
include/drm/drm_vblank.h | 22 ++++++++++++++++++
3 files changed, 71 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 28cdcf76b6f99..d1859bcc7ccbc 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
write_sequnlock(&vblank->seqlock);
}

+static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
+{
+ struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+ return vblank->max_vblank_count ?: dev->max_vblank_count;
+}
+
/*
* "No hw counter" fallback implementation of .get_vblank_counter() hook,
* if there is no useable hardware frame counter available.
*/
static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
{
- WARN_ON_ONCE(dev->max_vblank_count != 0);
+ WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
return 0;
}

@@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
ktime_t t_vblank;
int count = DRM_TIMESTAMP_MAXRETRIES;
int framedur_ns = vblank->framedur_ns;
+ u32 max_vblank_count = drm_max_vblank_count(dev, pipe);

/*
* Interrupts were disabled prior to this call, so deal with counter
@@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);

- if (dev->max_vblank_count != 0) {
+ if (max_vblank_count) {
/* trust the hw counter when it's around */
- diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
+ diff = (cur_vblank - vblank->last) & max_vblank_count;
} else if (rc && framedur_ns) {
u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));

@@ -1204,6 +1212,37 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
}
EXPORT_SYMBOL(drm_crtc_vblank_reset);

+/**
+ * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
+ * @crtc: CRTC in question
+ * @max_vblank_count: max hardware vblank counter value
+ *
+ * Update the maximum hardware vblank counter value for @crtc
+ * at runtime. Useful for hardware where the operation of the
+ * hardware vblank counter depends on the currently active
+ * display configuration.
+ *
+ * For example, if the hardware vblank counter does not work
+ * when a specific connector is active the maximum can be set
+ * to zero. And when that specific connector isn't active the
+ * maximum can again be set to the appropriate non-zero value.
+ *
+ * If used, must be called before drm_vblank_on().
+ */
+void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
+ u32 max_vblank_count)
+{
+ struct drm_device *dev = crtc->dev;
+ unsigned int pipe = drm_crtc_index(crtc);
+ struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+ WARN_ON(dev->max_vblank_count);
+ WARN_ON(!READ_ONCE(vblank->inmodeset));
+
+ vblank->max_vblank_count = max_vblank_count;
+}
+EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
+
/**
* drm_crtc_vblank_on - enable vblank events on a CRTC
* @crtc: CRTC in question
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index f9c6e0e3aec7d..fa117e11458ae 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -174,7 +174,13 @@ struct drm_device {
* races and imprecision over longer time periods, hence exposing a
* hardware vblank counter is always recommended.
*
- * If non-zeor, &drm_crtc_funcs.get_vblank_counter must be set.
+ * This is the statically configured device wide maximum. The driver
+ * can instead choose to use a runtime configurable per-crtc value
+ * &drm_vblank_crtc.max_vblank_count, in which case @max_vblank_count
+ * must be left at zero. See drm_crtc_set_max_vblank_count() on how
+ * to use the per-crtc value.
+ *
+ * If non-zero, &drm_crtc_funcs.get_vblank_counter must be set.
*/
u32 max_vblank_count; /**< size of vblank counter register */

diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index d25a9603ab570..e9c676381fd4f 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -128,6 +128,26 @@ struct drm_vblank_crtc {
* @last: Protected by &drm_device.vbl_lock, used for wraparound handling.
*/
u32 last;
+ /**
+ * @max_vblank_count:
+ *
+ * Maximum value of the vblank registers for this crtc. This value +1
+ * will result in a wrap-around of the vblank register. It is used
+ * by the vblank core to handle wrap-arounds.
+ *
+ * If set to zero the vblank core will try to guess the elapsed vblanks
+ * between times when the vblank interrupt is disabled through
+ * high-precision timestamps. That approach is suffering from small
+ * races and imprecision over longer time periods, hence exposing a
+ * hardware vblank counter is always recommended.
+ *
+ * This is the runtime configurable per-crtc maximum set through
+ * drm_crtc_set_max_vblank_count(). If this is used the driver
+ * must leave the device wide &drm_device.max_vblank_count at zero.
+ *
+ * If non-zero, &drm_crtc_funcs.get_vblank_counter must be set.
+ */
+ u32 max_vblank_count;
/**
* @inmodeset: Tracks whether the vblank is disabled due to a modeset.
* For legacy driver bit 2 additionally tracks whether an additional
@@ -206,4 +226,6 @@ bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
void drm_calc_timestamping_constants(struct drm_crtc *crtc,
const struct drm_display_mode *mode);
wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
+void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
+ u32 max_vblank_count);
#endif
--
2.20.1
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