arm64: Floating point and SIMD

This patch adds support for FP/ASIMD register bank saving and restoring
during context switch and FP exception handling to generate SIGFPE.
There are 32 128-bit registers and the context switching is currently
done non-lazily. Benchmarks on real hardware are required before
implementing lazy FP state saving/restoring.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

2 files changed, 186 insertions, 0 deletions

diff --git a/arch/arm64/kernel/entry-fpsimd.S b/arch/arm64/kernel/entry-fpsimd.S
new file mode 100644
index 000000000000..17988a6e7ea2
--- /dev/null
+++ b/arch/arm64/kernel/entry-fpsimd.S
@@ -0,0 +1,80 @@
+/*
+ * FP/SIMD state saving and restoring
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/assembler.h>
+
+/*
+ * Save the FP registers.
+ *
+ * x0 - pointer to struct fpsimd_state
+ */
+ENTRY(fpsimd_save_state)
+        stp     q0, q1, [x0, #16 * 0]
+        stp     q2, q3, [x0, #16 * 2]
+        stp     q4, q5, [x0, #16 * 4]
+        stp     q6, q7, [x0, #16 * 6]
+        stp     q8, q9, [x0, #16 * 8]
+        stp     q10, q11, [x0, #16 * 10]
+        stp     q12, q13, [x0, #16 * 12]
+        stp     q14, q15, [x0, #16 * 14]
+        stp     q16, q17, [x0, #16 * 16]
+        stp     q18, q19, [x0, #16 * 18]
+        stp     q20, q21, [x0, #16 * 20]
+        stp     q22, q23, [x0, #16 * 22]
+        stp     q24, q25, [x0, #16 * 24]
+        stp     q26, q27, [x0, #16 * 26]
+        stp     q28, q29, [x0, #16 * 28]
+        stp     q30, q31, [x0, #16 * 30]!
+        mrs     x8, fpsr
+        str     w8, [x0, #16 * 2]
+        mrs     x8, fpcr
+        str     w8, [x0, #16 * 2 + 4]
+        ret
+ENDPROC(fpsimd_save_state)
+
+/*
+ * Load the FP registers.
+ *
+ * x0 - pointer to struct fpsimd_state
+ */
+ENTRY(fpsimd_load_state)
+        ldp     q0, q1, [x0, #16 * 0]
+        ldp     q2, q3, [x0, #16 * 2]
+        ldp     q4, q5, [x0, #16 * 4]
+        ldp     q6, q7, [x0, #16 * 6]
+        ldp     q8, q9, [x0, #16 * 8]
+        ldp     q10, q11, [x0, #16 * 10]
+        ldp     q12, q13, [x0, #16 * 12]
+        ldp     q14, q15, [x0, #16 * 14]
+        ldp     q16, q17, [x0, #16 * 16]
+        ldp     q18, q19, [x0, #16 * 18]
+        ldp     q20, q21, [x0, #16 * 20]
+        ldp     q22, q23, [x0, #16 * 22]
+        ldp     q24, q25, [x0, #16 * 24]
+        ldp     q26, q27, [x0, #16 * 26]
+        ldp     q28, q29, [x0, #16 * 28]
+        ldp     q30, q31, [x0, #16 * 30]!
+        ldr     w8, [x0, #16 * 2]
+        ldr     w9, [x0, #16 * 2 + 4]
+        msr     fpsr, x8
+        msr     fpcr, x9
+        ret
+ENDPROC(fpsimd_load_state)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
new file mode 100644
index 000000000000..e8b8357aedb4
--- /dev/null
+++ b/arch/arm64/kernel/fpsimd.c
@@ -0,0 +1,106 @@
+/*
+ * FP/SIMD context switching and fault handling
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+
+#include <asm/fpsimd.h>
+#include <asm/cputype.h>
+
+#define FPEXC_IOF       (1 << 0)
+#define FPEXC_DZF       (1 << 1)
+#define FPEXC_OFF       (1 << 2)
+#define FPEXC_UFF       (1 << 3)
+#define FPEXC_IXF       (1 << 4)
+#define FPEXC_IDF       (1 << 7)
+
+/*
+ * Trapped FP/ASIMD access.
+ */
+void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
+{
+        /* TODO: implement lazy context saving/restoring */
+        WARN_ON(1);
+}
+
+/*
+ * Raise a SIGFPE for the current process.
+ */
+void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
+{
+        siginfo_t info;
+        unsigned int si_code = 0;
+
+        if (esr & FPEXC_IOF)
+                si_code = FPE_FLTINV;
+        else if (esr & FPEXC_DZF)
+                si_code = FPE_FLTDIV;
+        else if (esr & FPEXC_OFF)
+                si_code = FPE_FLTOVF;
+        else if (esr & FPEXC_UFF)
+                si_code = FPE_FLTUND;
+        else if (esr & FPEXC_IXF)
+                si_code = FPE_FLTRES;
+
+        memset(&info, 0, sizeof(info));
+        info.si_signo = SIGFPE;
+        info.si_code = si_code;
+        info.si_addr = (void __user *)instruction_pointer(regs);
+
+        send_sig_info(SIGFPE, &info, current);
+}
+
+void fpsimd_thread_switch(struct task_struct *next)
+{
+        /* check if not kernel threads */
+        if (current->mm)
+                fpsimd_save_state(&current->thread.fpsimd_state);
+        if (next->mm)
+                fpsimd_load_state(&next->thread.fpsimd_state);
+}
+
+void fpsimd_flush_thread(void)
+{
+        memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
+        fpsimd_load_state(&current->thread.fpsimd_state);
+}
+
+/*
+ * FP/SIMD support code initialisation.
+ */
+static int __init fpsimd_init(void)
+{
+        u64 pfr = read_cpuid(ID_AA64PFR0_EL1);
+
+        if (pfr & (0xf << 16)) {
+                pr_notice("Floating-point is not implemented\n");
+                return 0;
+        }
+        elf_hwcap |= HWCAP_FP;
+
+        if (pfr & (0xf << 20))
+                pr_notice("Advanced SIMD is not implemented\n");
+        else
+                elf_hwcap |= HWCAP_ASIMD;
+
+        return 0;
+}
+late_initcall(fpsimd_init);