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David S. Miller [Tue, 22 Jan 2013 19:47:13 +0000 (14:47 -0500)]

Merge branch 'legacy-isa-delete' of git://git./linux/kernel/git/paulg/linux

Paul Gortmaker says:

====================
The Ethernet-HowTo was maintained for roughly 10 years, from 1993 to 2003.
Fortunately sane hardware probing and auto detection (via PCI and ISA/PnP)
largely made the document a relic of the past, hence it being abandoned
a decade ago.

However, there is one last useful thing that we can extract from the
effort made in maintaining that document.  We can use it to guide us
with respect to what rare, experimental and/or super ancient 10Mbit
ISA drivers don't make sense to maintain in-tree anymore.

Nobody will argue that ISA is obsolete.  Availability went away at about
the time Pentium3 motherboards moved from 500MHz Slot1/SECC processors
to the green 500MHz Socket 370 Pentium3 chips, at the turn of the century.

In theory, it is possible that someone could still be running one of these
12+ year old P3 machines and want 3.9+ bleeding edge kernels (but unlikely).
In light of the above (remote) possibility, we can defer the removal of some
ISA network drivers that were highly popular and well tested.  Typically
that means the stuff more from the mid to late '90s, some with ISA PnP
support, like the 3c509, the wd/SMC 8390 based stuff, PCnet/lance etc.

But a lot of other drivers, typically from the early 1990s were for rare
hardware, and experimental (to the point of requiring a cron job that would
do a test ping, and then ifconfig down/up and/or a rmmod/insmod!).  And
some of these drivers (znet, and lp486e to name two) are physically tied
to platforms with on motherboard ethernet -- of 486 machines that date
from the early 1990s and can only have single digit amounts of memory.

What I'd like to achieve here with this series, is to get rid of those old
drivers that are no longer being used.  In an earlier discussion where
I'd proposed deleting a single driver, Alan suggested we instead dump
all the historical stuff in one go, to make it "...immediately obvious
where the break point is..."[1] and that it was "perfectly reasonable it
(and a pile of other ISA cards) ought to be shown the door"[2].  So that
is the goal here - make a clear line in the sand where the really ancient
stuff finally gets kicked to the curb.

Two old parallel port drivers are considered for removal here as well,
since in early 386/486 ISA machines, the parallel port was typically found
with the UARTS on the multi-I/O ISA controller card.  These drivers also date
from the early 1990's; parallel ports are no longer found on modern boards,
and their performance was not even capable of 10% of 10Mbit bandwidth.

Allow me a preemptive justification against the inevitable comments from
well meaning bystanders who suggest "why not just leave all this alone?".
Dead drivers cost us all if they are left in tree.  If you think that
is false, then please first consider:

-every time you type "git status", you are checking to see if modifications
have been made by you to all that dead code.

-every time you type "git grep <regex>" you are searching through files
which contain that dead code that simply does not interest you.

-every time you build a "allyesconfig" and an "allmodconfig" (don't tell
me you skip this step before submitting your changes to a maintainer),
you waste CPU cycles building this dead code.

-every time there is a tree wide API change, or cleanup, or file relocation,
we pay the cost of updating dead code, or moving dead code.

-daily regression tests (take linux-next as the most transparent
example) spend time building (and possibly running) this dead code.

-hard working people who regularly run auditing tools looking for lurking
bugs (sparse/coverity/smatch/coccinelle) are wasting time checking for,
and fixing bugs in this dead code.

This last one is key.  Please take a look at the git history for the
files that are proposed for removal here.  Look at the git history for
any one of them ("git whatchanged --follow drivers/net/.../driver.c")
Mentally sort the changes into two bins -- (1) the robotic tree-wide
changes, and (2) the "look I found a real run-time bug while using this"
category.  You will see that category #2 is essentially empty.

Further to that, realize that drivers don't simply disappear.  We are
not operating in the binary-only distribution space like other OS.  All
these drivers remain in the git history forever.  If a person is an
enthusiast for extreme legacy hardware, they are probably already
customizing their kernel source and building it themselves to support
such systems.  Also keep in mind that they could still build the 3.8
kernel exactly as-is, and run it (or a 3.8.x stable variant of it) for
several more years if they were really determined to cling to these old
experimental ISA drivers for some reason.

In summary, I hope that folks can be pragmatic about this, and not
get swept up in nostalgia.  Ask yourself whether it is realistic to
expect a person would have a genuine use case where they would
need to build a 3.9+ modern kernel and install it on some legacy hardware
that has no option but to absolutely _require_ one of the drivers
that are deleted here.

The following series was created with --irreversible-delete for
ease of review (it skips showing the content of files that are
deleted); however the complete patches can be pulled as per below.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>