+ * Contains common data for Rx and Tx queues.
+ *
+ * Note the difference between n_bd and n_window: the hardware
+ * always assumes 256 descriptors, so n_bd is always 256 (unless
+ * there might be HW changes in the future). For the normal TX
+ * queues, n_window, which is the size of the software queue data
+ * is also 256; however, for the command queue, n_window is only
+ * 32 since we don't need so many commands pending. Since the HW
+ * still uses 256 BDs for DMA though, n_bd stays 256. As a result,
+ * the software buffers (in the variables @meta, @txb in struct
+ * iwl_tx_queue) only have 32 entries, while the HW buffers (@tfds
+ * in the same struct) have 256.
+ * This means that we end up with the following:
+ * HW entries: | 0 | ... | N * 32 | ... | N * 32 + 31 | ... | 255 |
+ * SW entries: | 0 | ... | 31 |
+ * where N is a number between 0 and 7. This means that the SW
+ * data is a window overlayed over the HW queue.