sfc: rewrite efx_tx_may_pio

/* Report whether this TX queue would be empty for the given write_count.

 * May return false negative.

 */

static inline bool __efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue,

					 unsigned int write_count)

static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue, unsigned int write_count)

{

	unsigned int empty_read_count = READ_ONCE(tx_queue->empty_read_count);

	return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0;

}

/* Report whether the NIC considers this TX queue empty, using

 * packet_write_count (the write count recorded for the last completable

 * doorbell push).  May return false negative.  EF10 only, which is OK

 * because only EF10 supports PIO.

 */

static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue)

{

	EFX_WARN_ON_ONCE_PARANOID(!tx_queue->efx->type->option_descriptors);

	return __efx_nic_tx_is_empty(tx_queue, tx_queue->packet_write_count);

}

/* Get partner of a TX queue, seen as part of the same net core queue */

/* XXX is this a thing on EF100? */

static inline struct efx_tx_queue *efx_tx_queue_partner(struct efx_tx_queue *tx_queue)

		return tx_queue + EFX_TXQ_TYPE_OFFLOAD;

}

/* Decide whether we can use TX PIO, ie. write packet data directly into

 * a buffer on the device.  This can reduce latency at the expense of

 * throughput, so we only do this if both hardware and software TX rings

 * are empty.  This also ensures that only one packet at a time can be

 * using the PIO buffer.

 */

static inline bool efx_nic_may_tx_pio(struct efx_tx_queue *tx_queue)

{

	struct efx_tx_queue *partner = efx_tx_queue_partner(tx_queue);

	return tx_queue->piobuf && efx_nic_tx_is_empty(tx_queue) &&

	       efx_nic_tx_is_empty(partner);

}

int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, struct sk_buff *skb,

			bool *data_mapped);

static inline bool efx_nic_may_push_tx_desc(struct efx_tx_queue *tx_queue,

					    unsigned int write_count)

{

	bool was_empty = __efx_nic_tx_is_empty(tx_queue, write_count);

	bool was_empty = efx_nic_tx_is_empty(tx_queue, write_count);

	tx_queue->empty_read_count = 0;

	return was_empty && tx_queue->write_count - write_count == 1;

	++tx_queue->insert_count;

	return 0;

}

/* Decide whether we can use TX PIO, ie. write packet data directly into

 * a buffer on the device.  This can reduce latency at the expense of

 * throughput, so we only do this if both hardware and software TX rings

 * are empty, including all queues for the channel.  This also ensures that

 * only one packet at a time can be using the PIO buffer. If the xmit_more

 * flag is set then we don't use this - there'll be another packet along

 * shortly and we want to hold off the doorbell.

 */

static bool efx_tx_may_pio(struct efx_tx_queue *tx_queue)

{

	struct efx_channel *channel = tx_queue->channel;

	if (!tx_queue->piobuf)

		return false;

	EFX_WARN_ON_ONCE_PARANOID(!channel->efx->type->option_descriptors);

	efx_for_each_channel_tx_queue(tx_queue, channel)

		if (!efx_nic_tx_is_empty(tx_queue, tx_queue->packet_write_count))

			return false;

	return true;

}

#endif /* EFX_USE_PIO */

/* Send any pending traffic for a channel. xmit_more is shared across all

			goto err;

#ifdef EFX_USE_PIO

	} else if (skb_len <= efx_piobuf_size && !xmit_more &&

		   efx_nic_may_tx_pio(tx_queue)) {

		   efx_tx_may_pio(tx_queue)) {

		/* Use PIO for short packets with an empty queue. */

		if (efx_enqueue_skb_pio(tx_queue, skb))

			goto err;