cpu/hotplug: Provide knobs to control SMT
[GitHub/LineageOS/android_kernel_motorola_exynos9610.git] / Documentation / arm / firmware.txt
1 Interface for registering and calling firmware-specific operations for ARM.
2 ----
3 Written by Tomasz Figa <t.figa@samsung.com>
4
5 Some boards are running with secure firmware running in TrustZone secure
6 world, which changes the way some things have to be initialized. This makes
7 a need to provide an interface for such platforms to specify available firmware
8 operations and call them when needed.
9
10 Firmware operations can be specified by filling in a struct firmware_ops
11 with appropriate callbacks and then registering it with register_firmware_ops()
12 function.
13
14 void register_firmware_ops(const struct firmware_ops *ops)
15
16 The ops pointer must be non-NULL. More information about struct firmware_ops
17 and its members can be found in arch/arm/include/asm/firmware.h header.
18
19 There is a default, empty set of operations provided, so there is no need to
20 set anything if platform does not require firmware operations.
21
22 To call a firmware operation, a helper macro is provided
23
24 #define call_firmware_op(op, ...) \
25 ((firmware_ops->op) ? firmware_ops->op(__VA_ARGS__) : (-ENOSYS))
26
27 the macro checks if the operation is provided and calls it or otherwise returns
28 -ENOSYS to signal that given operation is not available (for example, to allow
29 fallback to legacy operation).
30
31 Example of registering firmware operations:
32
33 /* board file */
34
35 static int platformX_do_idle(void)
36 {
37 /* tell platformX firmware to enter idle */
38 return 0;
39 }
40
41 static int platformX_cpu_boot(int i)
42 {
43 /* tell platformX firmware to boot CPU i */
44 return 0;
45 }
46
47 static const struct firmware_ops platformX_firmware_ops = {
48 .do_idle = exynos_do_idle,
49 .cpu_boot = exynos_cpu_boot,
50 /* other operations not available on platformX */
51 };
52
53 /* init_early callback of machine descriptor */
54 static void __init board_init_early(void)
55 {
56 register_firmware_ops(&platformX_firmware_ops);
57 }
58
59 Example of using a firmware operation:
60
61 /* some platform code, e.g. SMP initialization */
62
63 __raw_writel(__pa_symbol(exynos4_secondary_startup),
64 CPU1_BOOT_REG);
65
66 /* Call Exynos specific smc call */
67 if (call_firmware_op(cpu_boot, cpu) == -ENOSYS)
68 cpu_boot_legacy(...); /* Try legacy way */
69
70 gic_raise_softirq(cpumask_of(cpu), 1);