Enabling write-combining may also enable read reordering.  The BIU is
only guaranteed to read from a 128-bit CSR or 64-bit SRAM word when
the host reads from its lowest address; otherwise the BIU may use the
latched value.  Therefore we need to reinstate the read memory
barriers after the first read operation for each CSR or SRAM word.

Signed-off-by; Ben Hutchings <bhutchings@solarflare.com>

Based on work by Neil Turton <nturton@solarflare.com> and
Kieran Mansley <kmansley@solarflare.com>.

The BIU has now been verified to handle 3- and 4-dword writes within a
single 128-bit register correctly.  This means we can enable write-
combining and only insert write barriers between writes to distinct
registers.

This has been observed to save about 0.5 us when pushing a TX
descriptor to an empty TX queue.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

It is not necessary to serialise writes to the paged 128-bit
registers.  However, if we don't then we must always write the last
dword separately, not as part of a qword write.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

Document exactly which registers and functions have special behaviour,
and why races on writes to descriptor pointers are safe.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

Replace EFX_ERR() with netif_err(), EFX_INFO() with netif_info(),
EFX_LOG() with netif_dbg() and EFX_TRACE() and EFX_REGDUMP() with
netif_vdbg().

Replace EFX_ERR_RL(), EFX_INFO_RL() and EFX_LOG_RL() using explicit
calls to net_ratelimit().

Implement the ethtool operations to get and set message level flags,
and add a 'debug' module parameter for the initial value.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Acked-by: NJeff Garzik <jgarzik@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

While we're at it, use type suffixes of 'd', 'q' and 'o', consistent
with register type names.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>