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; }