1 // SPDX-License-Identifier: GPL-2.0
2 
3 #include <linux/efi.h>
4 #include <asm/efi.h>
5 
6 #include "efistub.h"
7 
8 /*
9  * There are two ways of populating the core kernel's struct screen_info via the stub:
10  * - using a configuration table, like below, which relies on the EFI init code
11  *   to locate the table and copy the contents;
12  * - by linking directly to the core kernel's copy of the global symbol.
13  *
14  * The latter is preferred because it makes the EFIFB earlycon available very
15  * early, but it only works if the EFI stub is part of the core kernel image
16  * itself. The zboot decompressor can only use the configuration table
17  * approach.
18  *
19  * In order to support both methods from the same build of the EFI stub
20  * library, provide this dummy global definition of struct screen_info. If it
21  * is required to satisfy a link dependency, it means we need to override the
22  * __weak alloc and free methods with the ones below, and those will be pulled
23  * in as well.
24  */
25 struct screen_info screen_info;
26 
27 static efi_guid_t screen_info_guid = LINUX_EFI_SCREEN_INFO_TABLE_GUID;
28 
29 struct screen_info *alloc_screen_info(void)
30 {
31 	struct screen_info *si;
32 	efi_status_t status;
33 
34 	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
35 			     sizeof(*si), (void **)&si);
36 
37 	if (status != EFI_SUCCESS)
38 		return NULL;
39 
40 	status = efi_bs_call(install_configuration_table,
41 			     &screen_info_guid, si);
42 	if (status == EFI_SUCCESS)
43 		return si;
44 
45 	efi_bs_call(free_pool, si);
46 	return NULL;
47 }
48 
49 void free_screen_info(struct screen_info *si)
50 {
51 	if (!si)
52 		return;
53 
54 	efi_bs_call(install_configuration_table, &screen_info_guid, NULL);
55 	efi_bs_call(free_pool, si);
56 }
57