[PATCH 13/14] drm/i915: Use binary search when looking for shadowed registers

Tvrtko Ursulin tursulin at ursulin.net
Tue Oct 4 08:29:28 UTC 2016


From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Simply replace the linear search with the kernel's binary
search implementation. There is only six registers currently
in that table so this may not be that interesting. It adds a
function call so hopefully remains performance neutral for now.

v2: No need for manual conversion to bool for return.
    (Joonas Lahtinen)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_uncore.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index d7c9b6bc6e5e..8ac684598cec 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -691,14 +691,30 @@ static void intel_shadow_table_check(void)
 	}
 }
 
+static int mmio_reg_cmp(const void *key, const void *elt)
+{
+	u32 offset = (u32)(unsigned long)key;
+	i915_reg_t *reg = (i915_reg_t *)elt;
+
+	if (offset < i915_mmio_reg_offset(*reg))
+		return -1;
+	else if (offset > i915_mmio_reg_offset(*reg))
+		return 1;
+	else
+		return 0;
+}
+
 static bool is_gen8_shadowed(u32 offset)
 {
-	int i;
-	for (i = 0; i < ARRAY_SIZE(gen8_shadowed_regs); i++)
-		if (offset == gen8_shadowed_regs[i].reg)
-			return true;
+	i915_reg_t *reg;
 
-	return false;
+	reg = bsearch((void *)(unsigned long)offset,
+		      (const void *)gen8_shadowed_regs,
+		      ARRAY_SIZE(gen8_shadowed_regs),
+		      sizeof(i915_reg_t),
+		      mmio_reg_cmp);
+
+	return reg;
 }
 
 #define __gen8_reg_write_fw_domains(offset) \
-- 
2.7.4



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