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Documentation / arm / firmware.txt




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Based on kernel version 4.0. Page generated on 2015-04-14 21:19 EST.

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(virt_to_phys(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);
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