MIPS: Tidy up FPU context switching

Rather than saving the scalar FP or vector context in the assembly
resume function, reuse the existing C code we have in fpu.h to do
exactly that. This reduces duplication, results in a much easier to read
resume function & should allow the compiler to optimise out more MSA
code due to is_msa_enabled()/cpu_has_msa being known-zero at compile
time for kernels without MSA support.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-kernel@vger.kernel.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Manuel Lauss <manuel.lauss@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/10830/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/fpu.h

@@ -164,25 +164,30 @@ static inline int own_fpu(int restore)
 	return ret;
 }
 
-static inline void lose_fpu(int save)
+static inline void lose_fpu_inatomic(int save, struct task_struct *tsk)
 {
-	preempt_disable();
 	if (is_msa_enabled()) {
 		if (save) {
-			save_msa(current);
+			save_msa(tsk);
-			current->thread.fpu.fcr31 =
+			tsk->thread.fpu.fcr31 =
 					read_32bit_cp1_register(CP1_STATUS);
 		}
 		disable_msa();
-		clear_thread_flag(TIF_USEDMSA);
+		clear_tsk_thread_flag(tsk, TIF_USEDMSA);
 		__disable_fpu();
 	} else if (is_fpu_owner()) {
 		if (save)
-			_save_fp(current);
+			_save_fp(tsk);
 		__disable_fpu();
 	}
-	KSTK_STATUS(current) &= ~ST0_CU1;
+	KSTK_STATUS(tsk) &= ~ST0_CU1;
-	clear_thread_flag(TIF_USEDFPU);
+	clear_tsk_thread_flag(tsk, TIF_USEDFPU);
+}
+
+static inline void lose_fpu(int save)
+{
+	preempt_disable();
+	lose_fpu_inatomic(save, current);
 	preempt_enable();
 }
 

arch/mips/include/asm/switch_to.h

@@ -16,29 +16,21 @@
 #include <asm/watch.h>
 #include <asm/dsp.h>
 #include <asm/cop2.h>
-#include <asm/msa.h>
+#include <asm/fpu.h>
 
 struct task_struct;
 
-enum {
-	FP_SAVE_NONE	= 0,
-	FP_SAVE_VECTOR	= -1,
-	FP_SAVE_SCALAR	= 1,
-};
-
 /**
  * resume - resume execution of a task
  * @prev:	The task previously executed.
  * @next:	The task to begin executing.
  * @next_ti:	task_thread_info(next).
- * @fp_save:	Which, if any, FP context to save for prev.
  *
  * This function is used whilst scheduling to save the context of prev & load
  * the context of next. Returns prev.
  */
 extern asmlinkage struct task_struct *resume(struct task_struct *prev,
-		struct task_struct *next, struct thread_info *next_ti,
+		struct task_struct *next, struct thread_info *next_ti);
-		s32 fp_save);
 
 extern unsigned int ll_bit;
 extern struct task_struct *ll_task;
@@ -91,8 +83,8 @@ do {	if (cpu_has_rw_llb) {						\
  */
 #define switch_to(prev, next, last)					\
 do {									\
-	s32 __fpsave = FP_SAVE_NONE;					\
 	__mips_mt_fpaff_switch_to(prev);				\
+	lose_fpu_inatomic(1, prev);					\
 	if (cpu_has_dsp) {						\
 		__save_dsp(prev);					\
 		__restore_dsp(next);					\
@@ -111,15 +103,10 @@ do {									\
 		clear_c0_status(ST0_CU2);				\
 	}								\
 	__clear_software_ll_bit();					\
-	if (test_and_clear_tsk_thread_flag(prev, TIF_USEDFPU))		\
-		__fpsave = FP_SAVE_SCALAR;				\
-	if (test_and_clear_tsk_thread_flag(prev, TIF_USEDMSA))		\
-		__fpsave = FP_SAVE_VECTOR;				\
 	if (cpu_has_userlocal)						\
 		write_c0_userlocal(task_thread_info(next)->tp_value);	\
 	__restore_watch();						\
-	disable_msa();							\
+	(last) = resume(prev, next, task_thread_info(next));		\
-	(last) = resume(prev, next, task_thread_info(next), __fpsave);	\
 } while (0)
 
 #endif /* _ASM_SWITCH_TO_H */

arch/mips/kernel/r4k_switch.S

@@ -34,7 +34,7 @@
 #ifndef USE_ALTERNATE_RESUME_IMPL
 /*
  * task_struct *resume(task_struct *prev, task_struct *next,
- *		       struct thread_info *next_ti, s32 fp_save)
+ *		       struct thread_info *next_ti)
  */
 	.align	5
 	LEAF(resume)
@@ -43,45 +43,6 @@
 	cpu_save_nonscratch a0
 	LONG_S	ra, THREAD_REG31(a0)
 
-	/*
-	 * Check whether we need to save any FP context. FP context is saved
-	 * iff the process has used the context with the scalar FPU or the MSA
-	 * ASE in the current time slice, as indicated by _TIF_USEDFPU and
-	 * _TIF_USEDMSA respectively. switch_to will have set fp_save
-	 * accordingly to an FP_SAVE_ enum value.
-	 */
-	beqz	a3, 2f
-
-	/*
-	 * We do. Clear the saved CU1 bit for prev, such that next time it is
-	 * scheduled it will start in userland with the FPU disabled. If the
-	 * task uses the FPU then it will be enabled again via the do_cpu trap.
-	 * This allows us to lazily restore the FP context.
-	 */
-	PTR_L	t3, TASK_THREAD_INFO(a0)
-	LONG_L	t0, ST_OFF(t3)
-	li	t1, ~ST0_CU1
-	and	t0, t0, t1
-	LONG_S	t0, ST_OFF(t3)
-
-	/* Check whether we're saving scalar or vector context. */
-	bgtz	a3, 1f
-
-	/* Save 128b MSA vector context + scalar FP control & status. */
-	.set push
-	SET_HARDFLOAT
-	cfc1	t1, fcr31
-	msa_save_all	a0
-	.set pop	/* SET_HARDFLOAT */
-
-	sw	t1, THREAD_FCR31(a0)
-	b	2f
-
-1:	/* Save 32b/64b scalar FP context. */
-	fpu_save_double a0 t0 t1		# c0_status passed in t0
-						# clobbers t1
-2:
-
 #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
 	PTR_LA	t8, __stack_chk_guard
 	LONG_L	t9, TASK_STACK_CANARY(a1)