sfc: add MCDI tracing

This patchset adds support for logging MCDI (Management-Controller-to-
Driver Interface) interactions between the sfc driver and a bound device, to aid in debugging.
Solarflare has a tool to decode the resulting traces and will look to
open-source this if there is any external interest, but the protocol is already detailed in drivers/net/ethernet/sfc/mcdi_pcol.h.
The logging buffer we allocate per MCDI context is a work area for
constructing each individual message before logging it with netif_info.
The reason the buffer is long-lived is simply to avoid the overhead of
allocating and freeing it every MCDI call, since MCDIs are already known to be serialised for other reasons.

--
v4: remove patch #4, which has already been applied via sshah
v3: add some explanations to cover letter and patch #4
v2: avoid long lines in cover letter; fix multiline comment style

Edward Cree (3):
sfc: add tracing of MCDI commands
sfc: add sysfs entry to control MCDI tracing
sfc: add module parameter to enable MCDI logging on new functions

 drivers/net/ethernet/sfc/Kconfig |   9 ++++
 drivers/net/ethernet/sfc/ef10.c  |   3 ++
 drivers/net/ethernet/sfc/efx.c   |  49 ++++++++++++++++---
 drivers/net/ethernet/sfc/mcdi.c  | 100 +++++++++++++++++++++++++++++++++++++--
 drivers/net/ethernet/sfc/mcdi.h  |   6 +++
 5 files changed, 156 insertions(+), 11 deletions(-)