drm/i915: use the gmbus irq for waits
We need two special things to properly wire this up:
- Add another argument to gmbus_wait_hw_status to pass in the
correct interrupt bit in gmbus4.
- Since we can only get an irq for one of the two events we want,
hand-roll the wait_event_timeout code so that we wake up every
jiffie and can check for NAKs. This way we also subsume gmbus
support for platforms without interrupts (or where those are not
yet enabled).
The important bit really is to only enable one gmbus interrupt source
at the same time - with that piece of lore figured out, this seems to
work flawlessly.
Ben Widawsky rightfully complained the lack of measurements for the
claimed benefits (especially since the first version was actually
broken and fell back to bit-banging). Previously reading the 256 byte
hdmi EDID takes about 72 ms here. With this patch it's down to 33 ms.
Given that transfering the 256 bytes over i2c at wire speed takes
20.5ms alone, the reduction in additional overhead is rather nice.
v2: Chris Wilson wondered whether GMBUS4 might contain some set bits
when booting up an hence result in some spurious interrupts. Since we
clear GMBUS4 after every wait and we do gmbus transfer really early in
the setup sequence to detect displays the window is small, but still
be paranoid and clear it properly.
v3: Clarify the comment that gmbus irq generation can only support one
kind of event, why it bothers us and how we work around that limit.
Cc: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e7411f3..3843383 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -641,6 +641,7 @@
struct intel_gmbus gmbus[GMBUS_NUM_PORTS];
+
/** gmbus_mutex protects against concurrent usage of the single hw gmbus
* controller on different i2c buses. */
struct mutex gmbus_mutex;
@@ -650,6 +651,8 @@
*/
uint32_t gpio_mmio_base;
+ wait_queue_head_t gmbus_wait_queue;
+
struct pci_dev *bridge_dev;
struct intel_ring_buffer ring[I915_NUM_RINGS];
uint32_t next_seqno;