[PATCH v2 07/40] drm: Add a simple generator of random permutations

[Chris Wilson]

When testing, we want a random but yet reproducible order in which to
process elements. Here we create an array which is a random (using the
Tausworthe PRNG) permutation of the order in which to execute.

v2: Tidier code by David Herrmann

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: David Herrmann <dh.herrmann at gmail.com>
---
 drivers/gpu/drm/Kconfig          |  6 ++++++
 drivers/gpu/drm/Makefile         |  1 +
 drivers/gpu/drm/lib/drm_random.c | 41 ++++++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/lib/drm_random.h | 21 ++++++++++++++++++++
 4 files changed, 69 insertions(+)
 create mode 100644 drivers/gpu/drm/lib/drm_random.c
 create mode 100644 drivers/gpu/drm/lib/drm_random.h

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index d1363d21d3d1..2e6ae95459e4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -52,6 +52,7 @@ config DRM_DEBUG_MM_SELFTEST
 	tristate "kselftests for DRM range manager (struct drm_mm)"
 	depends on DRM
 	depends on DEBUG_KERNEL
+	select DRM_LIB_RANDOM
 	default n
 	help
 	  This option provides a kernel module that can be used to test
@@ -334,3 +335,8 @@ config DRM_SAVAGE
 	  chipset. If M is selected the module will be called savage.
 
 endif # DRM_LEGACY
+
+config DRM_LIB_RANDOM
+	bool
+	default n
+
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index c8aed3688b20..0fa16275fdae 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -18,6 +18,7 @@ drm-y       :=	drm_auth.o drm_bufs.o drm_cache.o \
 		drm_plane.o drm_color_mgmt.o drm_print.o \
 		drm_dumb_buffers.o drm_mode_config.o
 
+drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 obj-$(CONFIG_DRM_DEBUG_MM_SELFTEST) += selftests/test-drm_mm.o
 
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
diff --git a/drivers/gpu/drm/lib/drm_random.c b/drivers/gpu/drm/lib/drm_random.c
new file mode 100644
index 000000000000..507e72721b6f
--- /dev/null
+++ b/drivers/gpu/drm/lib/drm_random.c
@@ -0,0 +1,41 @@
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include "drm_random.h"
+
+static inline u32 prandom_u32_max_state(u32 ep_ro, struct rnd_state *state)
+{
+	return upper_32_bits((u64)prandom_u32_state(state) * ep_ro);
+}
+
+void drm_random_reorder(unsigned int *order, unsigned int count,
+			struct rnd_state *state)
+{
+	unsigned int i, j;
+
+	for (i = 0; i < count; ++i) {
+		BUILD_BUG_ON(sizeof(unsigned int) > sizeof(u32));
+		j = prandom_u32_max_state(count, state);
+		swap(order[i], order[j]);
+	}
+}
+EXPORT_SYMBOL(drm_random_reorder);
+
+unsigned int *drm_random_order(unsigned int count, struct rnd_state *state)
+{
+	unsigned int *order, i;
+
+	order = kmalloc_array(count, sizeof(*order), GFP_TEMPORARY);
+	if (!order)
+		return order;
+
+	for (i = 0; i < count; i++)
+		order[i] = i;
+
+	drm_random_reorder(order, count, state);
+	return order;
+}
+EXPORT_SYMBOL(drm_random_order);
diff --git a/drivers/gpu/drm/lib/drm_random.h b/drivers/gpu/drm/lib/drm_random.h
new file mode 100644
index 000000000000..931c8f4a261d
--- /dev/null
+++ b/drivers/gpu/drm/lib/drm_random.h
@@ -0,0 +1,21 @@
+#ifndef __DRM_RANDOM_H__
+#define __DRM_RANDOM_H
+
+#include <linux/random.h>
+
+#define RND_STATE_INITIALIZER(seed__) ({				\
+	struct rnd_state state__;					\
+	prandom_seed_state(&state__, (seed__));				\
+	state__;							\
+})
+
+#define RND_STATE(name__, seed__) \
+	struct rnd_state name__ = RND_STATE_INITIALIZER(seed__)
+
+unsigned int *drm_random_order(unsigned int count,
+			       struct rnd_state *state);
+void drm_random_reorder(unsigned int *order,
+			unsigned int count,
+			struct rnd_state *state);
+
+#endif /* __DRM_RANDOM_H__ */
-- 
2.11.0