MIPS: Simplify FP context initialization

MIPS has up until now had 3 different ways for a task's floating point
context to be initialized:

  - If the task's first use of FP involves it gaining ownership of an
    FPU then _init_fpu() is used to initialize the FPU's registers such
    that they all contain ~0, and the FPU registers will be stored to
    struct thread_info later (eg. when context switching).

  - If the task first uses FP on a CPU without an associated FPU then
    fpu_emulator_init_fpu() initializes the task's floating point
    register state in struct thread_info such that all floating point
    register contain the bit pattern 0x7ff800007ff80000, different to
    the _init_fpu() behaviour.

  - If a task's floating point context is first accessed via ptrace then
    init_fp_ctx() initializes the floating point register state in
    struct thread_info to ~0, giving equivalent state to _init_fpu().

The _init_fpu() path has 2 separate implementations - one for r2k/r3k
style systems & one for r4k style systems. The _init_fpu() path also
requires that we be careful to clear & restore the value of the
Config5.FRE bit on modern systems in order to avoid inadvertently
triggering floating point exceptions.

None of this code is in a performance critical hot path - it runs only
the first time a task uses floating point. As such it doesn't seem to
warrant the complications of maintaining the _init_fpu() path.

Remove _init_fpu() & fpu_emulator_init_fpu(), instead using
init_fp_ctx() consistently to initialize floating point register state
in struct thread_info. Upon a task's first use of floating point this
will typically mean that we initialize state in memory & then load it
into FPU registers using _restore_fp() just as we would on a context
switch. For other paths such as __compute_return_epc_for_insn() or
mipsr2_decoder() this results in a significant simplification of the
work to be done.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21002/
Cc: linux-mips@linux-mips.org

1 files changed, 0 insertions, 19 deletions

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index e5ba56c01ee0..04db951b0f8c 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -50,25 +50,6 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
 
-static void init_fp_ctx(struct task_struct *target)
-{
-	/* If FP has been used then the target already has context */
-	if (tsk_used_math(target))
-		return;
-
-	/* Begin with data registers set to all 1s... */
-	memset(&target->thread.fpu.fpr, ~0, sizeof(target->thread.fpu.fpr));
-
-	/* FCSR has been preset by `mips_set_personality_nan'.  */
-
-	/*
-	 * Record that the target has "used" math, such that the context
-	 * just initialised, and any modifications made by the caller,
-	 * aren't discarded.
-	 */
-	set_stopped_child_used_math(target);
-}
-
 /*
  * Called by kernel/ptrace.c when detaching..
  *