drm/i915: Add some selftests for sg_table manipulation

Start exercising the scattergather lists, especially looking at
iteration after coalescing.

v2: Comment on the peculiarity of table construction (i.e. why this
sg_table might be interesting).
v3: Added one __func__ to identify expect_pfn_sg()
v4: Loop until we have crossed the chain boundary (forcing sg_table to
do multiple allocations) before squelching a potential ENOMEM from oom.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170213171558.20942-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -2224,17 +2224,17 @@ unlock:
 	mutex_unlock(&obj->mm.lock);
 }
 
-static void i915_sg_trim(struct sg_table *orig_st)
+static bool i915_sg_trim(struct sg_table *orig_st)
 {
 	struct sg_table new_st;
 	struct scatterlist *sg, *new_sg;
 	unsigned int i;
 
 	if (orig_st->nents == orig_st->orig_nents)
-		return;
+		return false;
 
 	if (sg_alloc_table(&new_st, orig_st->nents, GFP_KERNEL | __GFP_NOWARN))
-		return;
+		return false;
 
 	new_sg = new_st.sgl;
 	for_each_sg(orig_st->sgl, sg, orig_st->nents, i) {
@@ -2247,6 +2247,7 @@ static void i915_sg_trim(struct sg_table *orig_st)
 	sg_free_table(orig_st);
 
 	*orig_st = new_st;
+	return true;
 }
 
 static struct sg_table *
@@ -5019,3 +5020,7 @@ i915_gem_object_get_dma_address(struct drm_i915_gem_object *obj,
 	sg = i915_gem_object_get_sg(obj, n, &offset);
 	return sg_dma_address(sg) + (offset << PAGE_SHIFT);
 }
+
+#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
+#include "selftests/scatterlist.c"
+#endif

drivers/gpu/drm/i915/selftests/i915_mock_selftests.h

@@ -9,3 +9,4 @@
  * Tests are executed in order by igt/drv_selftest
  */
 selftest(sanitycheck, i915_mock_sanitycheck) /* keep first (igt selfcheck) */
+selftest(scatterlist, scatterlist_mock_selftests)

drivers/gpu/drm/i915/selftests/scatterlist.c

@@ -0,0 +1,355 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/prime_numbers.h>
+#include <linux/random.h>
+
+#include "../i915_selftest.h"
+
+#define PFN_BIAS (1 << 10)
+
+struct pfn_table {
+	struct sg_table st;
+	unsigned long start, end;
+};
+
+typedef unsigned int (*npages_fn_t)(unsigned long n,
+				    unsigned long count,
+				    struct rnd_state *rnd);
+
+static noinline int expect_pfn_sg(struct pfn_table *pt,
+				  npages_fn_t npages_fn,
+				  struct rnd_state *rnd,
+				  const char *who,
+				  unsigned long timeout)
+{
+	struct scatterlist *sg;
+	unsigned long pfn, n;
+
+	pfn = pt->start;
+	for_each_sg(pt->st.sgl, sg, pt->st.nents, n) {
+		struct page *page = sg_page(sg);
+		unsigned int npages = npages_fn(n, pt->st.nents, rnd);
+
+		if (page_to_pfn(page) != pfn) {
+			pr_err("%s: %s left pages out of order, expected pfn %lu, found pfn %lu (using for_each_sg)\n",
+			       __func__, who, pfn, page_to_pfn(page));
+			return -EINVAL;
+		}
+
+		if (sg->length != npages * PAGE_SIZE) {
+			pr_err("%s: %s copied wrong sg length, expected size %lu, found %u (using for_each_sg)\n",
+			       __func__, who, npages * PAGE_SIZE, sg->length);
+			return -EINVAL;
+		}
+
+		if (igt_timeout(timeout, "%s timed out\n", who))
+			return -EINTR;
+
+		pfn += npages;
+	}
+	if (pfn != pt->end) {
+		pr_err("%s: %s finished on wrong pfn, expected %lu, found %lu\n",
+		       __func__, who, pt->end, pfn);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static noinline int expect_pfn_sg_page_iter(struct pfn_table *pt,
+					    const char *who,
+					    unsigned long timeout)
+{
+	struct sg_page_iter sgiter;
+	unsigned long pfn;
+
+	pfn = pt->start;
+	for_each_sg_page(pt->st.sgl, &sgiter, pt->st.nents, 0) {
+		struct page *page = sg_page_iter_page(&sgiter);
+
+		if (page != pfn_to_page(pfn)) {
+			pr_err("%s: %s left pages out of order, expected pfn %lu, found pfn %lu (using for_each_sg_page)\n",
+			       __func__, who, pfn, page_to_pfn(page));
+			return -EINVAL;
+		}
+
+		if (igt_timeout(timeout, "%s timed out\n", who))
+			return -EINTR;
+
+		pfn++;
+	}
+	if (pfn != pt->end) {
+		pr_err("%s: %s finished on wrong pfn, expected %lu, found %lu\n",
+		       __func__, who, pt->end, pfn);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static noinline int expect_pfn_sgtiter(struct pfn_table *pt,
+				       const char *who,
+				       unsigned long timeout)
+{
+	struct sgt_iter sgt;
+	struct page *page;
+	unsigned long pfn;
+
+	pfn = pt->start;
+	for_each_sgt_page(page, sgt, &pt->st) {
+		if (page != pfn_to_page(pfn)) {
+			pr_err("%s: %s left pages out of order, expected pfn %lu, found pfn %lu (using for_each_sgt_page)\n",
+			       __func__, who, pfn, page_to_pfn(page));
+			return -EINVAL;
+		}
+
+		if (igt_timeout(timeout, "%s timed out\n", who))
+			return -EINTR;
+
+		pfn++;
+	}
+	if (pfn != pt->end) {
+		pr_err("%s: %s finished on wrong pfn, expected %lu, found %lu\n",
+		       __func__, who, pt->end, pfn);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int expect_pfn_sgtable(struct pfn_table *pt,
+			      npages_fn_t npages_fn,
+			      struct rnd_state *rnd,
+			      const char *who,
+			      unsigned long timeout)
+{
+	int err;
+
+	err = expect_pfn_sg(pt, npages_fn, rnd, who, timeout);
+	if (err)
+		return err;
+
+	err = expect_pfn_sg_page_iter(pt, who, timeout);
+	if (err)
+		return err;
+
+	err = expect_pfn_sgtiter(pt, who, timeout);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static unsigned int one(unsigned long n,
+			unsigned long count,
+			struct rnd_state *rnd)
+{
+	return 1;
+}
+
+static unsigned int grow(unsigned long n,
+			 unsigned long count,
+			 struct rnd_state *rnd)
+{
+	return n + 1;
+}
+
+static unsigned int shrink(unsigned long n,
+			   unsigned long count,
+			   struct rnd_state *rnd)
+{
+	return count - n;
+}
+
+static unsigned int random(unsigned long n,
+			   unsigned long count,
+			   struct rnd_state *rnd)
+{
+	return 1 + (prandom_u32_state(rnd) % 1024);
+}
+
+static int alloc_table(struct pfn_table *pt,
+		       unsigned long count, unsigned long max,
+		       npages_fn_t npages_fn,
+		       struct rnd_state *rnd,
+		       int alloc_error)
+{
+	struct scatterlist *sg;
+	unsigned long n, pfn;
+
+	if (sg_alloc_table(&pt->st, max,
+			   GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN))
+		return alloc_error;
+
+	/* count should be less than 20 to prevent overflowing sg->length */
+	GEM_BUG_ON(overflows_type(count * PAGE_SIZE, sg->length));
+
+	/* Construct a table where each scatterlist contains different number
+	 * of entries. The idea is to check that we can iterate the individual
+	 * pages from inside the coalesced lists.
+	 */
+	pt->start = PFN_BIAS;
+	pfn = pt->start;
+	sg = pt->st.sgl;
+	for (n = 0; n < count; n++) {
+		unsigned long npages = npages_fn(n, count, rnd);
+
+		/* Nobody expects the Sparse Memmap! */
+		if (pfn_to_page(pfn + npages) != pfn_to_page(pfn) + npages) {
+			sg_free_table(&pt->st);
+			return -ENOSPC;
+		}
+
+		if (n)
+			sg = sg_next(sg);
+		sg_set_page(sg, pfn_to_page(pfn), npages * PAGE_SIZE, 0);
+
+		GEM_BUG_ON(page_to_pfn(sg_page(sg)) != pfn);
+		GEM_BUG_ON(sg->length != npages * PAGE_SIZE);
+		GEM_BUG_ON(sg->offset != 0);
+
+		pfn += npages;
+	}
+	sg_mark_end(sg);
+	pt->st.nents = n;
+	pt->end = pfn;
+
+	return 0;
+}
+
+static const npages_fn_t npages_funcs[] = {
+	one,
+	grow,
+	shrink,
+	random,
+	NULL,
+};
+
+static int igt_sg_alloc(void *ignored)
+{
+	IGT_TIMEOUT(end_time);
+	const unsigned long max_order = 20; /* approximating a 4GiB object */
+	struct rnd_state prng;
+	unsigned long prime;
+	int alloc_error = -ENOMEM;
+
+	for_each_prime_number(prime, max_order) {
+		unsigned long size = BIT(prime);
+		int offset;
+
+		for (offset = -1; offset <= 1; offset++) {
+			unsigned long sz = size + offset;
+			const npages_fn_t *npages;
+			struct pfn_table pt;
+			int err;
+
+			for (npages = npages_funcs; *npages; npages++) {
+				prandom_seed_state(&prng,
+						   i915_selftest.random_seed);
+				err = alloc_table(&pt, sz, sz, *npages, &prng,
+						  alloc_error);
+				if (err == -ENOSPC)
+					break;
+				if (err)
+					return err;
+
+				prandom_seed_state(&prng,
+						   i915_selftest.random_seed);
+				err = expect_pfn_sgtable(&pt, *npages, &prng,
+							 "sg_alloc_table",
+							 end_time);
+				sg_free_table(&pt.st);
+				if (err)
+					return err;
+			}
+		}
+
+		/* Test at least one continuation before accepting oom */
+		if (size > SG_MAX_SINGLE_ALLOC)
+			alloc_error = -ENOSPC;
+	}
+
+	return 0;
+}
+
+static int igt_sg_trim(void *ignored)
+{
+	IGT_TIMEOUT(end_time);
+	const unsigned long max = PAGE_SIZE; /* not prime! */
+	struct pfn_table pt;
+	unsigned long prime;
+	int alloc_error = -ENOMEM;
+
+	for_each_prime_number(prime, max) {
+		const npages_fn_t *npages;
+		int err;
+
+		for (npages = npages_funcs; *npages; npages++) {
+			struct rnd_state prng;
+
+			prandom_seed_state(&prng, i915_selftest.random_seed);
+			err = alloc_table(&pt, prime, max, *npages, &prng,
+					  alloc_error);
+			if (err == -ENOSPC)
+				break;
+			if (err)
+				return err;
+
+			if (i915_sg_trim(&pt.st)) {
+				if (pt.st.orig_nents != prime ||
+				    pt.st.nents != prime) {
+					pr_err("i915_sg_trim failed (nents %u, orig_nents %u), expected %lu\n",
+					       pt.st.nents, pt.st.orig_nents, prime);
+					err = -EINVAL;
+				} else {
+					prandom_seed_state(&prng,
+							   i915_selftest.random_seed);
+					err = expect_pfn_sgtable(&pt,
+								 *npages, &prng,
+								 "i915_sg_trim",
+								 end_time);
+				}
+			}
+			sg_free_table(&pt.st);
+			if (err)
+				return err;
+		}
+
+		/* Test at least one continuation before accepting oom */
+		if (prime > SG_MAX_SINGLE_ALLOC)
+			alloc_error = -ENOSPC;
+	}
+
+	return 0;
+}
+
+int scatterlist_mock_selftests(void)
+{
+	static const struct i915_subtest tests[] = {
+		SUBTEST(igt_sg_alloc),
+		SUBTEST(igt_sg_trim),
+	};
+
+	return i915_subtests(tests, NULL);
+}