+static inline unsigned int ar_next_buffer_index(unsigned int index)
+{
+ return (index + 1) % AR_BUFFERS;
+}
+
+static inline unsigned int ar_prev_buffer_index(unsigned int index)
+{
+ return (index - 1 + AR_BUFFERS) % AR_BUFFERS;
+}
+
+static inline unsigned int ar_first_buffer_index(struct ar_context *ctx)
+{
+ return ar_next_buffer_index(ctx->last_buffer_index);
+}
+
+/*
+ * We search for the buffer that contains the last AR packet DMA data written
+ * by the controller.
+ */
+static unsigned int ar_search_last_active_buffer(struct ar_context *ctx,
+ unsigned int *buffer_offset)
+{
+ unsigned int i, next_i, last = ctx->last_buffer_index;
+ __le16 res_count, next_res_count;
+
+ i = ar_first_buffer_index(ctx);
+ res_count = ACCESS_ONCE(ctx->descriptors[i].res_count);
+
+ /* A buffer that is not yet completely filled must be the last one. */
+ while (i != last && res_count == 0) {
+
+ /* Peek at the next descriptor. */
+ next_i = ar_next_buffer_index(i);
+ rmb(); /* read descriptors in order */
+ next_res_count = ACCESS_ONCE(
+ ctx->descriptors[next_i].res_count);
+ /*
+ * If the next descriptor is still empty, we must stop at this
+ * descriptor.
+ */
+ if (next_res_count == cpu_to_le16(PAGE_SIZE)) {
+ /*
+ * The exception is when the DMA data for one packet is
+ * split over three buffers; in this case, the middle
+ * buffer's descriptor might be never updated by the
+ * controller and look still empty, and we have to peek
+ * at the third one.
+ */
+ if (MAX_AR_PACKET_SIZE > PAGE_SIZE && i != last) {
+ next_i = ar_next_buffer_index(next_i);
+ rmb();
+ next_res_count = ACCESS_ONCE(
+ ctx->descriptors[next_i].res_count);
+ if (next_res_count != cpu_to_le16(PAGE_SIZE))
+ goto next_buffer_is_active;
+ }
+
+ break;
+ }
+
+next_buffer_is_active:
+ i = next_i;
+ res_count = next_res_count;
+ }
+
+ rmb(); /* read res_count before the DMA data */
+
+ *buffer_offset = PAGE_SIZE - le16_to_cpu(res_count);
+ if (*buffer_offset > PAGE_SIZE) {
+ *buffer_offset = 0;
+ ar_context_abort(ctx, "corrupted descriptor");
+ }
+
+ return i;
+}
+
+static void ar_sync_buffers_for_cpu(struct ar_context *ctx,
+ unsigned int end_buffer_index,
+ unsigned int end_buffer_offset)