HelenOS sources

root/kernel/arch/arm32/src/fpu_context.c

DEFINITIONS

1. fpu_have_coprocessor_access
2. fpu_enable_coprocessor_access
3. fpu_init
4. fpu_setup
5. handle_if_fpu_exception
6. fpu_enable
7. fpu_disable
8. fpu_context_save
9. fpu_context_restore

/*
 * Copyright (c) 2012 Jan Vesely
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup kernel_arm32
 * @{
 */
/** @file
 *  @brief arm32 FPU context
 */

#include <fpu_context.h>
#include <arch.h>
#include <arch/types.h>
#include <arch/security_ext.h>
#include <arch/cp15.h>
#include <cpu.h>

#define FPSID_IMPLEMENTER(r)   ((r) >> 24)
#define FPSID_SW_ONLY_FLAG   (1 << 23)
#define FPSID_SUBACHITECTURE(r)   (((r) >> 16) & 0x7f)
#define FPSID_PART_NUMBER(r)   (((r) >> 8) & 0xff)
#define FPSID_VARIANT(r)   (((r) >> 4) 0xf)
#define FPSID_REVISION(r)   (((r) >> 0) 0xf)

enum {
        FPU_VFPv1 = 0x00,
        FPU_VFPv2_COMMONv1 = 0x01,
        FPU_VFPv3_COMMONv2 = 0x02,
        FPU_VFPv3_NO_COMMON = 0x3, /* Does not support fpu exc. traps */
        FPU_VFPv3_COMMONv3 = 0x4,
};

extern uint32_t fpsid_read(void);
extern uint32_t mvfr0_read(void);

enum {
        FPEXC_EX_FLAG = (1 << 31),
        FPEXC_ENABLED_FLAG = (1 << 30),
};
extern uint32_t fpexc_read(void);
extern void fpexc_write(uint32_t);

/** ARM Architecture Reference Manual ch. B4.1.58, p. B$-1551 */
enum {
        FPSCR_N_FLAG = (1 << 31),
        FPSCR_Z_FLAG = (1 << 30),
        FPSCR_C_FLAG = (1 << 29),
        FPSCR_V_FLAG = (1 << 28),
        FPSCR_QC_FLAG = (1 << 27),
        FPSCR_AHP_FLAG = (1 << 26),
        FPSCR_DN_FLAG = (1 << 25),
        FPSCR_FZ_FLAG = (1 << 24),
        FPSCR_ROUND_MODE_MASK = (0x3 << 22),
        FPSCR_ROUND_TO_NEAREST = (0x0 << 22),
        FPSCR_ROUND_TO_POS_INF = (0x1 << 22),
        FPSCR_ROUND_TO_NEG_INF = (0x2 << 22),
        FPSCR_ROUND_TO_ZERO = (0x3 << 22),
        FPSCR_STRIDE_MASK = (0x3 << 20),
        FPSCR_STRIDE_SHIFT = 20,
        FPSCR_LEN_MASK = (0x7 << 16),
        FPSCR_LEN_SHIFT = 16,
        FPSCR_DENORMAL_EN_FLAG = (1 << 15),
        FPSCR_INEXACT_EN_FLAG = (1 << 12),
        FPSCR_UNDERFLOW_EN_FLAG = (1 << 11),
        FPSCR_OVERFLOW_EN_FLAG = (1 << 10),
        FPSCR_ZERO_DIV_EN_FLAG = (1 << 9),
        FPSCR_INVALID_OP_EN_FLAG = (1 << 8),
        FPSCR_DENORMAL_FLAG = (1 << 7),
        FPSCR_INEXACT_FLAG = (1 << 4),
        FPSCR_UNDERFLOW_FLAG = (1 << 3),
        FPSCR_OVERLOW_FLAG = (1 << 2),
        FPSCR_DIV_ZERO_FLAG = (1 << 1),
        FPSCR_INVALID_OP_FLAG = (1 << 0),

        FPSCR_EN_ALL = FPSCR_DENORMAL_EN_FLAG | FPSCR_INEXACT_EN_FLAG | FPSCR_UNDERFLOW_EN_FLAG | FPSCR_OVERFLOW_EN_FLAG | FPSCR_ZERO_DIV_EN_FLAG | FPSCR_INVALID_OP_EN_FLAG,
};

extern uint32_t fpscr_read(void);
extern void fpscr_write(uint32_t);

extern void fpu_context_save_s32(fpu_context_t *);
extern void fpu_context_restore_s32(fpu_context_t *);
extern void fpu_context_save_d16(fpu_context_t *);
extern void fpu_context_restore_d16(fpu_context_t *);
extern void fpu_context_save_d32(fpu_context_t *);
extern void fpu_context_restore_d32(fpu_context_t *);

static void (*save_context)(fpu_context_t *ctx);
static void (*restore_context)(fpu_context_t *ctx);

static int fpu_have_coprocessor_access(void)
{
        /*
         * The register containing the information (CPACR) is not available
         * on armv6-. Rely on user decision to use CONFIG_FPU.
         */
#ifdef PROCESSOR_ARCH_armv7_a
        const uint32_t cpacr = CPACR_read();
        /*
         * FPU needs access to coprocessor 10 and 11.
         * Moreover, they need to have same access enabled
         */
        if (((cpacr & CPACR_CP_MASK(10)) != CPACR_CP_FULL_ACCESS(10)) &&
            ((cpacr & CPACR_CP_MASK(11)) != CPACR_CP_FULL_ACCESS(11))) {
                printf("No access to CP10 and CP11: %" PRIx32 "\n", cpacr);
                return 0;
        }
#endif

        return 1;
}

/** Enable coprocessor access. Turn both non-secure mode bit and generic access.
 * Cortex A8 Manual says:
 * "You must execute an Instruction Memory Barrier (IMB) sequence immediately
 * after an update of the Coprocessor Access Control Register, see Memory
 * Barriers in the ARM Architecture Reference Manual. You must not attempt to
 * execute any instructions that are affected by the change of access rights
 * between the IMB sequence and the register update."
 * Cortex a8 TRM ch. 3.2.27. c1, Coprocessor Access Control Register
 *
 * @note do we need to call secure monitor here?
 */
static void fpu_enable_coprocessor_access(void)
{
        /*
         * The register containing the information (CPACR) is not available
         * on armv6-. Rely on user decision to use CONFIG_FPU.
         */
#ifdef PROCESSOR_ARCH_armv7_a
        /* Allow coprocessor access */
        uint32_t cpacr = CPACR_read();
        /*
         * FPU needs access to coprocessor 10 and 11.
         * Moreover, they need to have same access enabled
         */
        cpacr &= ~(CPACR_CP_MASK(10) | CPACR_CP_MASK(11));
        cpacr |= (CPACR_CP_FULL_ACCESS(10) | CPACR_CP_FULL_ACCESS(11));
        CPACR_write(cpacr);
#endif
}

void fpu_init(void)
{
        /* Check if we have access */
        if (!fpu_have_coprocessor_access())
                return;

        /* Clear all fpu flags */
        fpexc_write(0);
        fpu_enable();
        /*
         * Mask all exception traps,
         * The bits are RAZ/WI on archs that don't support fpu exc traps.
         */
        fpscr_write(fpscr_read() & ~FPSCR_EN_ALL);
}

void fpu_setup(void)
{
        uint32_t mvfr0;

        /* Enable coprocessor access */
        fpu_enable_coprocessor_access();

        /* Check if we succeeded */
        if (!fpu_have_coprocessor_access())
                return;

        const uint32_t fpsid = fpsid_read();
        if (fpsid & FPSID_SW_ONLY_FLAG) {
                printf("No FPU avaiable\n");
                return;
        }
        switch (FPSID_SUBACHITECTURE(fpsid)) {
        case FPU_VFPv1:
                printf("Detected VFPv1\n");
                save_context = fpu_context_save_s32;
                restore_context = fpu_context_restore_s32;
                break;
        case FPU_VFPv2_COMMONv1:
                printf("Detected VFPv2\n");
                save_context = fpu_context_save_d16;
                restore_context = fpu_context_restore_d16;
                break;
        case FPU_VFPv3_COMMONv2:
        case FPU_VFPv3_NO_COMMON:
        case FPU_VFPv3_COMMONv3:
                mvfr0 = mvfr0_read();
                /* See page B4-1637 */
                if ((mvfr0 & 0xf) == 0x1) {
                        printf("Detected VFPv3+ with 16 regs\n");
                        save_context = fpu_context_save_d16;
                        restore_context = fpu_context_restore_d16;
                } else {
                        printf("Detected VFPv3+ with 32 regs\n");
                        save_context = fpu_context_save_d32;
                        restore_context = fpu_context_restore_d32;
                }
                break;
        }
}

bool handle_if_fpu_exception(void)
{
        /* Check if we have access */
        if (!fpu_have_coprocessor_access())
                return false;

        const uint32_t fpexc = fpexc_read();
        if (fpexc & FPEXC_ENABLED_FLAG) {
                const uint32_t fpscr = fpscr_read();
                printf("FPU exception\n"
                    "\tFPEXC: %" PRIx32 " FPSCR: %" PRIx32 "\n", fpexc, fpscr);
                return false;
        }
#ifdef CONFIG_FPU_LAZY
        scheduler_fpu_lazy_request();
        return true;
#else
        return false;
#endif
}

void fpu_enable(void)
{
        /* Check if we have access */
        if (!fpu_have_coprocessor_access())
                return;
        /* Enable FPU instructions */
        fpexc_write(fpexc_read() | FPEXC_ENABLED_FLAG);
}

void fpu_disable(void)
{
        /* Check if we have access */
        if (!fpu_have_coprocessor_access())
                return;
        /* Disable FPU instructions */
        fpexc_write(fpexc_read() & ~FPEXC_ENABLED_FLAG);
}

void fpu_context_save(fpu_context_t *ctx)
{
        /* This is only necessary if we enable fpu exceptions. */
#if 0
        const uint32_t fpexc = fpexc_read();

        if (fpexc & FPEXC_EX_FLAG) {
                printf("EX FPU flag is on, things will fail\n");
                //TODO implement common subarch context saving
        }
#endif
        if (save_context)
                save_context(ctx);
}

void fpu_context_restore(fpu_context_t *ctx)
{
        if (restore_context)
                restore_context(ctx);
}