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MIPS: Basic MSA context switching support

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This patch adds support for context switching the MSA vector registers.
These 128 bit vector registers are aliased with the FP registers - an
FP register accesses the least significant bits of the vector register
with which it is aliased (ie. the register with the same index). Due to
both this & the requirement that the scalar FPU must be 64-bit (FR=1) if
enabled at the same time as MSA the kernel will enable MSA & scalar FP
at the same time for tasks which use MSA. If we restore the MSA vector
context then we might as well enable the scalar FPU since the reason it
was left disabled was to allow for lazy FP context restoring - but we
just restored the FP context as it's a subset of the vector context. If
we restore the FP context and have previously used MSA then we have to
restore the whole vector context anyway (see comment in
enable_restore_fp_context for details) so similarly we might as well
enable MSA.

Thus if a task does not use MSA then it will continue to behave as
without this patch - the scalar FP context will be saved & restored as
usual. But if a task executes an MSA instruction then it will save &
restore the vector context forever more.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6431/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2014-01-27 15:23:11 +00:00 • committed by Ralf Baechle
parent a5e9a69e2c
commit 1db1af84d6
10 changed files with 275 additions and 34 deletions
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7
arch/mips/kernel/process.c
View file

@ -32,6 +32,7 @@
#include <asm/cpu.h>
#include <asm/dsp.h>
#include <asm/fpu.h>
#include <asm/msa.h>
#include <asm/pgtable.h>
#include <asm/mipsregs.h>
#include <asm/processor.h>
@ -65,6 +66,8 @@ void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
clear_used_math();
clear_fpu_owner();
init_dsp();
clear_thread_flag(TIF_MSA_CTX_LIVE);
disable_msa();
regs->cp0_epc = pc;
regs->regs[29] = sp;
}
@ -89,7 +92,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
preempt_disable();
if (is_fpu_owner())
if (is_msa_enabled())
save_msa(p);
else if (is_fpu_owner())
save_fp(p);
if (cpu_has_dsp)