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 using struct firmware_ops
  11
  12         struct firmware_ops {
  13                 /*
  14                 * Enters CPU idle mode
  15                 */
  16                 int (*do_idle)(void);
  17                 /*
  18                 * Sets boot address of specified physical CPU
  19                 */
  20                 int (*set_cpu_boot_addr)(int cpu, unsigned long boot_addr);
  21                 /*
  22                 * Boots specified physical CPU
  23                 */
  24                 int (*cpu_boot)(int cpu);
  25                 /*
  26                 * Initializes L2 cache
  27                 */
  28                 int (*l2x0_init)(void);
  29         };
  30
  31 and then registered with register_firmware_ops function
  32
  33         void register_firmware_ops(const struct firmware_ops *ops)
  34
  35 the ops pointer must be non-NULL.
  36
  37 There is a default, empty set of operations provided, so there is no need to
  38 set anything if platform does not require firmware operations.
  39
  40 To call a firmware operation, a helper macro is provided
  41
  42         #define call_firmware_op(op, ...)                               \
  43                 ((firmware_ops->op) ? firmware_ops->op(__VA_ARGS__) : (-ENOSYS))
  44
  45 the macro checks if the operation is provided and calls it or otherwise returns
  46 -ENOSYS to signal that given operation is not available (for example, to allow
  47 fallback to legacy operation).
  48
  49 Example of registering firmware operations:
  50
  51         /* board file */
  52
  53         static int platformX_do_idle(void)
  54         {
  55                 /* tell platformX firmware to enter idle */
  56                 return 0;
  57         }
  58
  59         static int platformX_cpu_boot(int i)
  60         {
  61                 /* tell platformX firmware to boot CPU i */
  62                 return 0;
  63         }
  64
  65         static const struct firmware_ops platformX_firmware_ops = {
  66                 .do_idle        = exynos_do_idle,
  67                 .cpu_boot       = exynos_cpu_boot,
  68                 /* other operations not available on platformX */
  69         };
  70
  71         /* init_early callback of machine descriptor */
  72         static void __init board_init_early(void)
  73         {
  74                 register_firmware_ops(&platformX_firmware_ops);
  75         }
  76
  77 Example of using a firmware operation:
  78
  79         /* some platform code, e.g. SMP initialization */
  80
  81         __raw_writel(virt_to_phys(exynos4_secondary_startup),
  82                 CPU1_BOOT_REG);
  83
  84         /* Call Exynos specific smc call */
  85         if (call_firmware_op(cpu_boot, cpu) == -ENOSYS)
  86                 cpu_boot_legacy(...); /* Try legacy way */
  87
  88         gic_raise_softirq(cpumask_of(cpu), 1);