Correct a performance bug from Bill Paul's original FreeBSD bge(4) driver:

Each call to the FreeBSD bge_start() routine the transmit producer
pointer index from the chip mailbox register BGE_MBX_TX_HOST_PROD0_LO.
The local copy of that value is then updated by bge_encap() as
bge_encap() encapsulates packets in the Tx ring. If bge_encap()
succeds in encpuslating one or more packets, bge_start() tells the
chip to start sending the newly-encinitiates writes the new value back
to the chip mailbox register.

However, comparison of the Linux drivers (Broadcom-supplied and
open-source tg3.c) and to the OpenSolaris driver confirms that
register BGE_MBX_TX_HOST_PROD0_LO is write-only to software.
Thus, we can just keep a copy in the softc, and eliminate the
(expensive) PCI register write on each call to bge_start().

From jonathan NetBSD

tested by krw@, sturm@ and I on a few different bge NICs.

0 files changed, 0 insertions, 0 deletions