efi-framebuffer device的注册和显示参数的传递

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我是靠谱客的博主正直猫咪，最近开发中收集的这篇文章主要介绍efi-framebuffer device的注册和显示参数的传递，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

在drivers/firmware/efi/linstub/arm-stub.c 中efi_entry 中会调用setup_graphics
static struct screen_info *setup_graphics(efi_system_table_t *sys_table_arg)
{
   efi_guid_t gop_proto = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;
   efi_status_t status;
   unsigned long size;
   void **gop_handle = NULL;
   struct screen_info *si = NULL;

   size = 0;
   status = efi_call_early(locate_handle, EFI_LOCATE_BY_PROTOCOL,
               &gop_proto, NULL, &size, gop_handle);
   if (status == EFI_BUFFER_TOO_SMALL) {
       si = alloc_screen_info(sys_table_arg);
       if (!si)
           return NULL;
       efi_setup_gop(sys_table_arg, si, &gop_proto, size);
   }
   return si;
}
在setup_graphics 中会parse bios 中传递过来的参数，并保存到si中。
然后在init_screen_info 中让screen_info指向si，这样screen_info中就保持从bios中传递过来的framebuffer的参数
static void __init init_screen_info(void)
{
   struct screen_info *si;

   if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
       si = early_memremap_ro(screen_info_table, sizeof(*si));
       if (!si) {
           pr_err("Could not map screen_info config tablen");
           return;
       }
       screen_info = *si;
       early_memunmap(si, sizeof(*si));

       /* dummycon on ARM needs non-zero values for columns/lines */
       screen_info.orig_video_cols = 80;
       screen_info.orig_video_lines = 25;
   }

   if (screen_info.orig_video_isVGA == VIDEO_TYPE_EFI &&
        memblock_is_map_memory(screen_info.lfb_base))
       memblock_mark_nomap(screen_info.lfb_base, screen_info.lfb_size);
}
最后会调用register_gop_device 来注册platform_device
static int __init register_gop_device(void)
{
   void *pd;

   if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI)
       return 0;

   pd = platform_device_register_data(NULL, "efi-framebuffer", 0,
                       &screen_info, sizeof(screen_info));
   return PTR_ERR_OR_ZERO(pd);
}
subsys_initcall(register_gop_device);

这样当用户打开CONFIG_FB_EFI的时候，就会生成/dev/fbn device。通过对这个device的read和read 就可以将画面显示到fbcon上。

static struct platform_driver efifb_driver = {
   .driver = {
       .name = "efi-framebuffer",
   },
   .probe = efifb_probe,
   .remove = efifb_remove,
};

builtin_platform_driver(efifb_driver);
efi-framebuffer 对应的driver是在/drivers/video/fbdev/efifb.c中。
其通过在efifb_probe中调用register_framebuffer来得到对console的控制权。