src/arch/x86/include/smm_call.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <stdint.h>
   4 #include <cpu/x86/smm.h>
   5
   6 /*
   7  * Call the APMC SMI handler that resides in SMM. First, the command and sub-command are stored
   8  * in eax, and the argument pointer is stored in ebx, then the command byte is written to the
   9  * APMC IO port to trigger the SMI. The APMC SMI handler then reads the command from the APMC
  10  * IO port and the contents of eax and ebx from the SMM state save area.
  11  *
  12  * static inline because the resulting assembly is often smaller than
  13  * the call sequence due to constant folding.
  14  */
  15 static inline u32 call_smm(u8 cmd, u8 subcmd, void *arg)
  16 {
  17         const uint16_t apmc_port = pm_acpi_smi_cmd_port();
  18         u32 res = 0;
  19         __asm__ __volatile__ (
  20                 "outb %%al, %%dx"
  21                 : "=a" (res)
  22                 : "a" ((subcmd << 8) | cmd),
  23                   "b" (arg),
  24                   "d" (apmc_port)
  25                 : "memory");
  26         return res;
  27 }