drm: Add a simple generator of random permutations

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.

Note these are simple helpers intended to be merged upstream in lib/

v2: Tidier code by David Herrmann
v3: Add reminder that this code is intended to be temporary, with at
least the bulk of the prandom changes going to lib/

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161222083641.2691-6-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index ebfe840..45a1c74 100644 (file)
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -321,3 +321,7 @@ 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 b9ae428..6bb4163 100644 (file)
--- 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-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o
 drm-$(CONFIG_PCI) += ati_pcigart.o

diff --git a/drivers/gpu/drm/lib/drm_random.c b/drivers/gpu/drm/lib/drm_random.c
new file mode 100644 (file)
index 0000000..7b12a68
--- /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 drm_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 = drm_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 (file)
index 0000000..a78644b
--- /dev/null
+++ b/drivers/gpu/drm/lib/drm_random.h
@@ -0,0 +1,25 @@
+#ifndef __DRM_RANDOM_H__
+#define __DRM_RANDOM_H__
+
+/* This is a temporary home for a couple of utility functions that should
+ * be transposed to lib/ at the earliest convenience.
+ */
+
+#include <linux/random.h>
+
+#define DRM_RND_STATE_INITIALIZER(seed__) ({                           \
+       struct rnd_state state__;                                       \
+       prandom_seed_state(&state__, (seed__));                         \
+       state__;                                                        \
+})
+
+#define DRM_RND_STATE(name__, seed__) \
+       struct rnd_state name__ = DRM_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__ */