dpaa/eth: fast-path single-page TX frame build

The TX SG-build loop in dpaa_eth_if_start_locked() walked page
boundaries with PAGE_MASK arithmetic even for buffers that lived
entirely within one page -- the common case, since MCLBYTES
is smaller than PAGE_SIZE.  Add a fast path that emits a single SGT
entry for wholly-in-one-page segments and skips the inner while
entirely.

Fix the following bugs while we're here:

1. "if (m->m_len == 0) continue;" in the outer loop never
   advanced m -- any zero-length mbuf hung the TX path in an
   infinite loop.  Fix this by switching to a for loop, with the
   advancement in the post-clause.

2. In the inner (page-splitting) loop, the cap
   "if (m->m_len < ssize) ssize = m->m_len;" compared against
   the mbuf's original length, not the remaining bytes.  A single mbuf
   whose data started mid-page and ran into a second page would produce
   a second SGT entry with ssize > rem, over-reading past the buffer end
   into whatever followed in kernel memory.  Fixed by tracking a local
   rem and capping ssize against it.

3. If the whole mbuf chain consisted of zero-length segments,
   the final-flag store "fi_sgt[i - 1].final = 1" wrote to
   index -1.  Reject empty frames up front now instead.

As part of this, rename the inner counter from dsize to rem for clarity
instead of playing double-duty in both inner and outer loops.

0 files changed, 0 insertions, 0 deletions