+/*
+ * Allocate a new buffer and add it to the list of free buffers for this
+ * context. Must be called with ohci->lock held.
+ */
+static int
+context_add_buffer(struct context *ctx)
+{
+ struct descriptor_buffer *desc;
+ dma_addr_t bus_addr;
+ int offset;
+
+ /*
+ * 16MB of descriptors should be far more than enough for any DMA
+ * program. This will catch run-away userspace or DoS attacks.
+ */
+ if (ctx->total_allocation >= 16*1024*1024)
+ return -ENOMEM;
+
+ desc = dma_alloc_coherent(ctx->ohci->card.device, PAGE_SIZE,
+ &bus_addr, GFP_ATOMIC);
+ if (!desc)
+ return -ENOMEM;
+
+ offset = (void *)&desc->buffer - (void *)desc;
+ desc->buffer_size = PAGE_SIZE - offset;
+ desc->buffer_bus = bus_addr + offset;
+ desc->used = 0;
+
+ list_add_tail(&desc->list, &ctx->buffer_list);
+ ctx->total_allocation += PAGE_SIZE;
+
+ return 0;
+}
+