From: Ville Syrjälä <[email protected]>
Stop using the heavier intel_uncore_{read,write}() and
just use intel_uncore_{read,write}_fw() for all display
register accesses.
The main functional change here is that we now stop
grabbing uncore.lock for display registers. Its job
is now fully taken over by the display mmio.lock.
The one little thing we want to keep from the uncore
implementation is the runtime pm asserts (sadly xe
doesn't implement them, but i915 does). We have the
parent interface for it, so just use it. That is one
extra vfunc call, but not sure there's any way around
it.
One somewhat unexpected side effect (or bonus) is that
on ILK we also lose ilk_dummy_write(), which is currently
done ahead of all (non-fw) mmio accesses. The only
purpose of the dummy write is to wake the GT from
RC6 ahead of the actual mmio access. Display has
nothing to do with RC6, and I don't think we actually
ever enabled RC6 on ILK, so the whole thing is pointless.
As a result of eliminating ilk_dummy_write() display
register accesses become faster on ILK (numbers in
nanoseconds):
| fw | non-fw |
read | 140 | 430 -> 140 |
write | 170 | 470 -> 170 |
Register accesses on TGL also get a bit faster,
compared against the original code before the
display mmio vfuncs were introduced:
| fw | non-fw | theoretical non-fw(*)
read | 230 | 970 -> 840 | 2*230+230 = 690
write | 100 | 820 -> 740 | 2*230+100 = 560
(*) two FPGA_DBG reads + the actual register access
I presume the improvement was due to some combination of
eliminating the extra debug lock and just reducing the
runtime overhead in general. The remaining delta between
theory and practice seems to be mostly due to mmio.lock.
We'll probably want to think of ways to eliminate the lock
entirely, on the platforms that don't need it for register
access serialization...
Signed-off-by: Ville Syrjälä <[email protected]>
---
drivers/gpu/drm/i915/display/intel_de.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_de.c
b/drivers/gpu/drm/i915/display/intel_de.c
index 0a51105e0fba..397145bc7e5b 100644
--- a/drivers/gpu/drm/i915/display/intel_de.c
+++ b/drivers/gpu/drm/i915/display/intel_de.c
@@ -9,6 +9,7 @@
#include "intel_de.h"
#include "intel_display_regs.h"
+#include "intel_display_rpm.h"
static int intel_de_wait_for_register(struct intel_display *display,
intel_reg_t reg, u32 mask, u32 value,
@@ -341,11 +342,13 @@ __intel_de_read(struct intel_display *display,
intel_reg_t reg,
unsigned long irqflags;
u32 val;
+ assert_display_rpm_held(display);
+
__mmio_wakelock_pre(display, reg, mmio_flags);
__mmio_lock_pre(display, &irqflags, mmio_flags);
__mmio_unclaimed_pre(display, reg, false, mmio_flags);
- val = intel_uncore_read(__to_uncore(display), reg);
+ val = intel_de_read_fw(display, reg);
__mmio_unclaimed_post(display, reg, false, mmio_flags);
__mmio_lock_post(display, irqflags, mmio_flags);
@@ -360,11 +363,13 @@ __intel_de_write(struct intel_display *display,
intel_reg_t reg, u32 val,
{
unsigned long irqflags;
+ assert_display_rpm_held(display);
+
__mmio_wakelock_pre(display, reg, mmio_flags);
__mmio_lock_pre(display, &irqflags, mmio_flags);
__mmio_unclaimed_pre(display, reg, true, mmio_flags);
- intel_uncore_write(__to_uncore(display), reg, val);
+ intel_de_write_fw(display, reg, val);
__mmio_unclaimed_post(display, reg, true, mmio_flags);
__mmio_lock_post(display, irqflags, mmio_flags);
--
2.56.0
