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kernel: arch: introduce k_float_enable()

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This patch introduce new API to enable FPU of thread. This is pair of
existed k_float_disable() API. And also add empty arch_float_enable()
into each architectures that have arch_float_disable(). The arc and
riscv already implemented arch_float_enable() so I do not touch
these implementations.

Motivation: Current Zephyr implementation does not allow to use FPU
on main and other system threads like as work queue. Users need to
create an other thread with K_FP_REGS for floating point programs.
Users can use FPU more easily if they can enable FPU on running
threads.

Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
This commit is contained in:
Katsuhiro Suzuki 2021-02-01 15:16:53 +09:00 • committed by Carles Cufí
commit 59903e2934
10 changed files with 93 additions and 34 deletions
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40
include/kernel.h
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@ -5544,6 +5544,46 @@ __syscall void k_str_out(char *c, size_t n);
*/
__syscall int k_float_disable(struct k_thread *thread);
/**
* @brief Enable preservation of floating point context information.
*
* This routine informs the kernel that the specified thread
* will use the floating point registers.
* Invoking this routine initializes the thread's floating point context info
* to that of an FPU that has been reset. The next time the thread is scheduled
* by z_swap() it will either inherit an FPU that is guaranteed to be in a
* "sane" state (if the most recent user of the FPU was cooperatively swapped
* out) or the thread's own floating point context will be loaded (if the most
* recent user of the FPU was preempted, or if this thread is the first user
* of the FPU). Thereafter, the kernel will protect the thread's FP context
* so that it is not altered during a preemptive context switch.
*
* The @a options parameter indicates which floating point register sets will
* be used by the specified thread.
*
* For x86 options:
*
* - K_FP_REGS indicates x87 FPU and MMX registers only
* - K_SSE_REGS indicates SSE registers (and also x87 FPU and MMX registers)
*
* @warning
* Some architectures apply restrictions on how the enabling of floating
* point preservation may be requested, see arch_float_enable.
*
* @warning
* This routine should only be used to enable floating point support for
* a thread that currently has such support enabled.
*
* @param thread ID of thread.
* @param options architecture dependent options
*
* @retval 0 On success.
* @retval -ENOTSUP If the floating point enabling is not implemented.
* -EINVAL If the floating point enabling could not be performed.
*/
__syscall int k_float_enable(struct k_thread *thread, unsigned int options);
#ifdef CONFIG_THREAD_RUNTIME_STATS
/**