[Intel-gfx] [PATCH] drm/i915: Assert that we don't overflow frontbuffer tracking bits

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Add some compile time assrts to the frontbuffer tracking to make sure
that we have enough bits per pipe to cover all the planes, and that we
have enough total bits to cover all the planes across all pipes.

We'll ignore any potential clash between the overlay bit and the
plane bits because that will allow us to keep using a total of 32
bits for the foreseeable future.

While at it change the macros to use BIT() and GENMASK(). The latter
gets rid of the hardcoded 0xff and thus means we can change the
number of bits per pipe by just changing
INTEL_FRONTBUFFER_BITS_PER_PIPE.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 454d8f937fae..98f346c7b0b3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2411,12 +2411,16 @@ enum hdmi_force_audio {
  * We have one bit per pipe and per scanout plane type.
  */
 #define INTEL_FRONTBUFFER_BITS_PER_PIPE 8
-#define INTEL_FRONTBUFFER(pipe, plane_id) \
-	(1 << ((plane_id) + INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
+#define INTEL_FRONTBUFFER(pipe, plane_id) ({ \
+	BUILD_BUG_ON(INTEL_FRONTBUFFER_BITS_PER_PIPE * I915_MAX_PIPES > 32); \
+	BUILD_BUG_ON(I915_MAX_PLANES > INTEL_FRONTBUFFER_BITS_PER_PIPE); \
+	BIT((plane_id) + INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)); \
+})
 #define INTEL_FRONTBUFFER_OVERLAY(pipe) \
-	(1 << (INTEL_FRONTBUFFER_BITS_PER_PIPE - 1 + INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
+	BIT(INTEL_FRONTBUFFER_BITS_PER_PIPE - 1 + INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe))
 #define INTEL_FRONTBUFFER_ALL_MASK(pipe) \
-	(0xff << (INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
+	GENMASK(INTEL_FRONTBUFFER_BITS_PER_PIPE * ((pipe) + 1) - 1, \
+		INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe))
 
 /*
  * Optimised SGL iterator for GEM objects
-- 
2.13.6