[PATCH v7 10/26] drm/i915/display: Do not take uncore lock in i915_get_vblank_counter

Maarten Lankhorst
2026-03-10T11:57:43Z

This fixes a lockdep splat that occurs in the code that should be run
with interrupts disabled. The uncore lock should not be taken and
released repeatedly in a timing sensitive path.

Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
---
drivers/gpu/drm/i915/display/intel_de.h | 8 ++++++
drivers/gpu/drm/i915/display/intel_vblank.c | 4 +--
drivers/gpu/drm/i915/intel_uncore.h | 26 +++++++++++++------
.../drm/xe/compat-i915-headers/intel_uncore.h | 7 +++++
4 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_de.h b/drivers/gpu/drm/i915/display/intel_de.h
index f30f3f8ebee1d..8990c2c778efe 100644
--- a/drivers/gpu/drm/i915/display/intel_de.h
+++ b/drivers/gpu/drm/i915/display/intel_de.h
@@ -68,6 +68,14 @@ intel_de_read64_2x32(struct intel_display *display,
return val;
}

+static inline u64
+intel_de_read64_2x32_fw(struct intel_display *display,
+ i915_reg_t lower_reg, i915_reg_t upper_reg)
+{
+ return intel_uncore_read64_2x32_fw(__to_uncore(display),
+ lower_reg, upper_reg);
+}
+
static inline void
intel_de_posting_read(struct intel_display *display, i915_reg_t reg)
{
diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index e204c260b9aef..749127ae7794c 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -109,8 +109,8 @@ u32 i915_get_vblank_counter(struct drm_crtc *crtc)
* we get a low value that's stable across two reads of the high
* register.
*/
- frame = intel_de_read64_2x32(display, PIPEFRAMEPIXEL(display, pipe),
- PIPEFRAME(display, pipe));
+ frame = intel_de_read64_2x32_fw(display, PIPEFRAMEPIXEL(display, pipe),
+ PIPEFRAME(display, pipe));

pixel = frame & PIPE_PIXEL_MASK;
frame = (frame >> PIPE_FRAME_LOW_SHIFT) & 0xffffff;
diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
index fafc2ca9a2376..507398a562649 100644
--- a/drivers/gpu/drm/i915/intel_uncore.h
+++ b/drivers/gpu/drm/i915/intel_uncore.h
@@ -449,13 +449,28 @@ static inline void intel_uncore_rmw_fw(struct intel_uncore *uncore,
intel_uncore_write_fw(uncore, reg, val);
}

+static inline u64
+intel_uncore_read64_2x32_fw(struct intel_uncore *uncore,
+ i915_reg_t lower_reg, i915_reg_t upper_reg)
+{
+ u32 upper, lower, old_upper, loop = 0;
+ upper = intel_uncore_read_fw(uncore, upper_reg);
+ do {
+ old_upper = upper;
+ lower = intel_uncore_read_fw(uncore, lower_reg);
+ upper = intel_uncore_read_fw(uncore, upper_reg);
+ } while (upper != old_upper && loop++ < 2);
+
+ return (u64)upper << 32 | lower;
+}
+
static inline u64
intel_uncore_read64_2x32(struct intel_uncore *uncore,
i915_reg_t lower_reg, i915_reg_t upper_reg)
{
- u32 upper, lower, old_upper, loop = 0;
enum forcewake_domains fw_domains;
unsigned long flags;
+ u64 ret;

fw_domains = intel_uncore_forcewake_for_reg(uncore, lower_reg,
FW_REG_READ);
@@ -466,17 +481,12 @@ intel_uncore_read64_2x32(struct intel_uncore *uncore,
spin_lock_irqsave(&uncore->lock, flags);
intel_uncore_forcewake_get__locked(uncore, fw_domains);

- upper = intel_uncore_read_fw(uncore, upper_reg);
- do {
- old_upper = upper;
- lower = intel_uncore_read_fw(uncore, lower_reg);
- upper = intel_uncore_read_fw(uncore, upper_reg);
- } while (upper != old_upper && loop++ < 2);
+ ret = intel_uncore_read64_2x32_fw(uncore, lower_reg, upper_reg);

intel_uncore_forcewake_put__locked(uncore, fw_domains);
spin_unlock_irqrestore(&uncore->lock, flags);

- return (u64)upper << 32 | lower;
+ return ret;
}

static inline int intel_uncore_write_and_verify(struct intel_uncore *uncore,
diff --git a/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h b/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
index a8cfd65119e09..6959a761fa06a 100644
--- a/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
+++ b/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
@@ -74,6 +74,13 @@ intel_uncore_read64_2x32(struct intel_uncore *uncore,
return (u64)upper << 32 | lower;
}

+static inline u64
+intel_uncore_read64_2x32_fw(struct intel_uncore *uncore,
+ i915_reg_t i915_lower_reg, i915_reg_t i915_upper_reg)
+{
+ return intel_uncore_read64_2x32(uncore, i915_lower_reg, i915_upper_reg);
+}
+
static inline void intel_uncore_posting_read(struct intel_uncore *uncore,
i915_reg_t i915_reg)
{
--
2.51.0