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Subject[PATCH 2/3] drm/i915: split out check for noncontiguous pfn range
Date
We get a warning with gcc-7 about a pointless comparison when
using a linear memmap:

drivers/gpu/drm/i915/selftests/scatterlist.c: In function 'alloc_table':
drivers/gpu/drm/i915/selftests/scatterlist.c:219:66: error: self-comparison always evaluates to false [-Werror=tautological-compare]

Splitting out the comparison into a separate function avoids the warning
and makes it slightly more obvious what happens.

Fixes: 935a2f776aa5 ("drm/i915: Add some selftests for sg_table manipulation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/gpu/drm/i915/selftests/scatterlist.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/selftests/scatterlist.c b/drivers/gpu/drm/i915/selftests/scatterlist.c
index eb2cda8e2b9f..c072b0f9180b 100644
--- a/drivers/gpu/drm/i915/selftests/scatterlist.c
+++ b/drivers/gpu/drm/i915/selftests/scatterlist.c
@@ -189,6 +189,11 @@ static unsigned int random(unsigned long n,
return 1 + (prandom_u32_state(rnd) % 1024);
}

+static inline bool page_contiguous(struct page *first, struct page *last, unsigned long npages)
+{
+ return first + npages == last;
+}
+
static int alloc_table(struct pfn_table *pt,
unsigned long count, unsigned long max,
npages_fn_t npages_fn,
@@ -216,7 +221,8 @@ static int alloc_table(struct pfn_table *pt,
unsigned long npages = npages_fn(n, count, rnd);

/* Nobody expects the Sparse Memmap! */
- if (pfn_to_page(pfn + npages) != pfn_to_page(pfn) + npages) {
+ if (!page_contiguous(pfn_to_page(pfn),
+ pfn_to_page(pfn + npages), npages)) {
sg_free_table(&pt->st);
return -ENOSPC;
}
--
2.9.0
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