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, 58 deletions

diff --git a/arch/mips/kernel/r2300_fpu.S b/arch/mips/kernel/r2300_fpu.S
index 3062ba66c563..12e58053544f 100644
--- a/arch/mips/kernel/r2300_fpu.S
+++ b/arch/mips/kernel/r2300_fpu.S
@@ -52,64 +52,6 @@ LEAF(_restore_fp)
 	jr	ra
 	END(_restore_fp)
 
-/*
- * Load the FPU with signalling NANS.  This bit pattern we're using has
- * the property that no matter whether considered as single or as double
- * precision represents signaling NANS.
- *
- * The value to initialize fcr31 to comes in $a0.
- */
-
-	.set push
-	SET_HARDFLOAT
-
-LEAF(_init_fpu)
-	mfc0	t0, CP0_STATUS
-	li	t1, ST0_CU1
-	or	t0, t1
-	mtc0	t0, CP0_STATUS
-
-	ctc1	a0, fcr31
-
-	li	t0, -1
-
-	mtc1	t0, $f0
-	mtc1	t0, $f1
-	mtc1	t0, $f2
-	mtc1	t0, $f3
-	mtc1	t0, $f4
-	mtc1	t0, $f5
-	mtc1	t0, $f6
-	mtc1	t0, $f7
-	mtc1	t0, $f8
-	mtc1	t0, $f9
-	mtc1	t0, $f10
-	mtc1	t0, $f11
-	mtc1	t0, $f12
-	mtc1	t0, $f13
-	mtc1	t0, $f14
-	mtc1	t0, $f15
-	mtc1	t0, $f16
-	mtc1	t0, $f17
-	mtc1	t0, $f18
-	mtc1	t0, $f19
-	mtc1	t0, $f20
-	mtc1	t0, $f21
-	mtc1	t0, $f22
-	mtc1	t0, $f23
-	mtc1	t0, $f24
-	mtc1	t0, $f25
-	mtc1	t0, $f26
-	mtc1	t0, $f27
-	mtc1	t0, $f28
-	mtc1	t0, $f29
-	mtc1	t0, $f30
-	mtc1	t0, $f31
-	jr	ra
-	END(_init_fpu)
-
-	.set pop
-
 	.set	noreorder
 
 /**