1/*
 2 * x86 FPU bug checks:
 3 */
 4#include <asm/fpu/internal.h>
 5
 6/*
 7 * Boot time CPU/FPU FDIV bug detection code:
 8 */
 9
10static double __initdata x = 4195835.0;
11static double __initdata y = 3145727.0;
12
13/*
14 * This used to check for exceptions..
15 * However, it turns out that to support that,
16 * the XMM trap handlers basically had to
17 * be buggy. So let's have a correct XMM trap
18 * handler, and forget about printing out
19 * some status at boot.
20 *
21 * We should really only care about bugs here
22 * anyway. Not features.
23 */
24static void __init check_fpu(void)
25{
26	u32 cr0_saved;
27	s32 fdiv_bug;
28
29	/* We might have CR0::TS set already, clear it: */
30	cr0_saved = read_cr0();
31	write_cr0(cr0_saved & ~X86_CR0_TS);
32
33	kernel_fpu_begin();
34
35	/*
36	 * trap_init() enabled FXSR and company _before_ testing for FP
37	 * problems here.
38	 *
39	 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug
40	 */
41	__asm__("fninit\n\t"
42		"fldl %1\n\t"
43		"fdivl %2\n\t"
44		"fmull %2\n\t"
45		"fldl %1\n\t"
46		"fsubp %%st,%%st(1)\n\t"
47		"fistpl %0\n\t"
48		"fwait\n\t"
49		"fninit"
50		: "=m" (*&fdiv_bug)
51		: "m" (*&x), "m" (*&y));
52
53	kernel_fpu_end();
54
55	write_cr0(cr0_saved);
56
57	if (fdiv_bug) {
58		set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
59		pr_warn("Hmm, FPU with FDIV bug\n");
60	}
61}
62
63void __init fpu__init_check_bugs(void)
64{
65	/*
66	 * kernel_fpu_begin/end() in check_fpu() relies on the patched
67	 * alternative instructions.
68	 */
69	if (cpu_has_fpu)
70		check_fpu();
71}