[patch] dma-pool: warn when coherent pool is depleted

[David Rientjes]

When a DMA coherent pool is depleted, allocation failures may or may not
get reported in the kernel log depending on the allocator.

The admin does have a workaround, however, by using coherent_pool= on the
kernel command line.

Provide some guidance on the failure and a recommended minimum size for
the pools (double the size).

Signed-off-by: David Rientjes <rient...@google.com>
---
 kernel/dma/pool.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
        }
 
        val = gen_pool_alloc(pool, size);
-       if (val) {
+       if (likely(val)) {
                phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
 
                *ret_page = pfn_to_page(__phys_to_pfn(phys));
                ptr = (void *)val;
                memset(ptr, 0, size);
+       } else {
+               WARN_ONCE(1, "DMA coherent pool depleted, increase size "
+                            "(recommended min coherent_pool=%zuK)\n",
+                         gen_pool_size(pool) >> 9);
        }
        if (gen_pool_avail(pool) < atomic_pool_size)
                schedule_work(&atomic_pool_work);