Function sgl_len

dpdk/drivers/net/cxgbe/sge.c:430–451

* sgl_len - calculates the size of an SGL of the given capacity * @n: the number of SGL entries * * Calculates the number of flits needed for a scatter/gather list that * can hold the given number of entries. */

 * can hold the given number of entries.
 */
static inline unsigned int sgl_len(unsigned int n)
{
	/*
	 * A Direct Scatter Gather List uses 32-bit lengths and 64-bit PCI DMA
	 * addresses.  The DSGL Work Request starts off with a 32-bit DSGL
	 * ULPTX header, then Length0, then Address0, then, for 1 <= i <= N,
	 * repeated sequences of { Length[i], Length[i+1], Address[i],
	 * Address[i+1] } (this ensures that all addresses are on 64-bit
	 * boundaries).  If N is even, then Length[N+1] should be set to 0 and
	 * Address[N+1] is omitted.
	 *
	 * The following calculation incorporates all of the above.  It's
	 * somewhat hard to follow but, briefly: the "+2" accounts for the
	 * first two flits which include the DSGL header, Length0 and
	 * Address0; the "(3*(n-1))/2" covers the main body of list entries (3
	 * flits for every pair of the remaining N) +1 if (n-1) is odd; and
	 * finally the "+((n-1)&1)" adds the one remaining flit needed if
	 * (n-1) is odd ...
	 */
	n--;
	return (3 * n) / 2 + (n & 1) + 2;
}

/**
 * flits_to_desc - returns the num of Tx descriptors for the given flits