misc: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
int stuff;
struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Link: https://lore.kernel.org/r/20200226222240.GA14474@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

gru: improve GRU TLB dropin statistics

Update the TLB dropin statistics kept for each GRU context. Count TLB
dropins separate from the misses - some misses do not result in a TLB
dropin. Some of the diagnostics need both counts.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: preload tlb for bcopy instructions

Add anticipatory TLB dropins for GRU TLB misses that occur on BCOPY
instructions that copy large amounts of data.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: add debug option for cache flushing

Add a debug option to the SGI GRU driver for flushing GRU cache lines from
memory. In theory this is not needed but it is useful for debugging.
This has no use by end users.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: allow users to specify gru chiplet 1

Add table & user request infrastructure that is needed to allow users to
specify the blade and chiplet for allocation of GRU contexts. Use of this
information is in a subsequent patch.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: fixes to grudump utility

Minor fixes to the SGI GRU grudump facility:
- fix address where user data is written
- add gru number to data passed to user
- indicate if context is locked

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: add user request to specify gru slice

Add a user request to specify the gru instruction slice parameter for user
contexts.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: generic infrastructure for context options

Change the user GRU request for specifying the "task_slice" option to use
a generic infrastructure that can be expanded in the future to include
additional context options. No new capabilities are added with this
patch.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: delete user request for fetching chiplet status

Delete the user request for fetching the status of a GRU chiplet. This
request has been made obsolete by other changes. Note: this is not a
change to a user API - there are no compatibility issues with this change.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: collect per-context user statistics

Collect GRU statistics for each user GRU context. Statistics are kept for
TLB misses & content resource contention. Add user request for retrieving
the statistics.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: update gru kernel self tests

Change the kernel self tests that can be optionally executed on GRU
initialization. This is primarily for testing.

Eliminate the BUG statements on failure and return bad status. Add ioctl
interface to execute the tests on demand.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

gru: dump chiplet state

Add support for dumpping the state of an entire GRU chiplet.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

GRU Driver: driver internal header files

This patch contains header files internal to the GRU driver.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>