1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Common code to handle absent "placeholder" devices 4 * Copyright 2001 Resilience Corporation <ebrower@resilience.com> 5 * 6 * This map driver is used to allocate "placeholder" MTD 7 * devices on systems that have socketed/removable media. 8 * Use of this driver as a fallback preserves the expected 9 * registration of MTD device nodes regardless of probe outcome. 10 * A usage example is as follows: 11 * 12 * my_dev[i] = do_map_probe("cfi", &my_map[i]); 13 * if(NULL == my_dev[i]) { 14 * my_dev[i] = do_map_probe("map_absent", &my_map[i]); 15 * } 16 * 17 * Any device 'probed' with this driver will return -ENODEV 18 * upon open. 19 */ 20 21 #include <linux/module.h> 22 #include <linux/types.h> 23 #include <linux/kernel.h> 24 #include <linux/errno.h> 25 #include <linux/slab.h> 26 #include <linux/init.h> 27 #include <linux/mtd/mtd.h> 28 #include <linux/mtd/map.h> 29 30 static int map_absent_read (struct mtd_info *, loff_t, size_t, size_t *, u_char *); 31 static int map_absent_write (struct mtd_info *, loff_t, size_t, size_t *, const u_char *); 32 static int map_absent_erase (struct mtd_info *, struct erase_info *); 33 static void map_absent_sync (struct mtd_info *); 34 static struct mtd_info *map_absent_probe(struct map_info *map); 35 static void map_absent_destroy (struct mtd_info *); 36 37 38 static struct mtd_chip_driver map_absent_chipdrv = { 39 .probe = map_absent_probe, 40 .destroy = map_absent_destroy, 41 .name = "map_absent", 42 .module = THIS_MODULE 43 }; 44 45 static struct mtd_info *map_absent_probe(struct map_info *map) 46 { 47 struct mtd_info *mtd; 48 49 mtd = kzalloc(sizeof(*mtd), GFP_KERNEL); 50 if (!mtd) { 51 return NULL; 52 } 53 54 map->fldrv = &map_absent_chipdrv; 55 mtd->priv = map; 56 mtd->name = map->name; 57 mtd->type = MTD_ABSENT; 58 mtd->size = map->size; 59 mtd->_erase = map_absent_erase; 60 mtd->_read = map_absent_read; 61 mtd->_write = map_absent_write; 62 mtd->_sync = map_absent_sync; 63 mtd->flags = 0; 64 mtd->erasesize = PAGE_SIZE; 65 mtd->writesize = 1; 66 67 __module_get(THIS_MODULE); 68 return mtd; 69 } 70 71 72 static int map_absent_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf) 73 { 74 return -ENODEV; 75 } 76 77 static int map_absent_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf) 78 { 79 return -ENODEV; 80 } 81 82 static int map_absent_erase(struct mtd_info *mtd, struct erase_info *instr) 83 { 84 return -ENODEV; 85 } 86 87 static void map_absent_sync(struct mtd_info *mtd) 88 { 89 /* nop */ 90 } 91 92 static void map_absent_destroy(struct mtd_info *mtd) 93 { 94 /* nop */ 95 } 96 97 static int __init map_absent_init(void) 98 { 99 register_mtd_chip_driver(&map_absent_chipdrv); 100 return 0; 101 } 102 103 static void __exit map_absent_exit(void) 104 { 105 unregister_mtd_chip_driver(&map_absent_chipdrv); 106 } 107 108 module_init(map_absent_init); 109 module_exit(map_absent_exit); 110 111 MODULE_LICENSE("GPL"); 112 MODULE_AUTHOR("Resilience Corporation - Eric Brower <ebrower@resilience.com>"); 113 MODULE_DESCRIPTION("Placeholder MTD chip driver for 'absent' chips"); 114