Use busybox devmem

buildroot_config_fragment

@@ -47,31 +47,6 @@ BR2_PACKAGE_DTC=y
 BR2_PACKAGE_DTC_PROGRAMS=y
 BR2_PACKAGE_HOST_DTC=y
 
-# On ARM, with our lkmc_platform_device:
-#
-#     devmem2 0x101e9000 w 0x12345678
-#
-# Then on QEMU monitor, notice that the registers don't actually change value:
-#
-#     xp/4 0x101e9000
-#
-# Uses /dev/mem.
-#
-# Upstream: http://free-electrons.com/pub/mirror/devmem2.c
-#
-# See also:
-#
-# - https://superuser.com/questions/71389/what-is-dev-mem/1214662#1214662
-# - https://unix.stackexchange.com/questions/4948/shell-command-to-read-device-registers
-# - man mem
-#
-# TODO: why with mmap MAP_PRIVATE (used in my previous custom naive version),
-# the entire register page is read?;
-#
-# TODO: have a look at: https://github.com/kaiwan/device-memory-readwrite
-#
-BR2_PACKAGE_DEVMEM2=y
-
 # Provides setpci and a lspci more advanced than Busybox's
 #
 # setpci can read and write to PCI configuration registers.

busybox_config_fragment

@@ -4,3 +4,25 @@ CONFIG_NC=y
 CONFIG_NC_EXTRA=y
 CONFIG_NC_SERVER=y
 CONFIG_STAT=y
+
+# On ARM, with our lkmc_platform_device:
+#
+#     devmem 0x101e9000 w 0x12345678
+#
+# Then on QEMU monitor, notice that the registers don't actually change value:
+#
+#     xp/4 0x101e9000
+#
+# Uses /dev/mem.
+#
+# See also:
+#
+# - https://superuser.com/questions/71389/what-is-dev-mem/1214662#1214662
+# - https://unix.stackexchange.com/questions/4948/shell-command-to-read-device-registers
+# - man mem
+#
+# TODO: why with mmap MAP_PRIVATE (used in my previous custom naive version),
+# the entire register page is read?;
+#
+# TODO: have a look at: https://github.com/kaiwan/device-memory-readwrite
+CONFIG_DEVMEM=y

kernel_module/character_device_create.c

@@ -1,7 +1,7 @@
 /*
 Automatically create the device under /dev on insmod, and remove on rmmod.
 
-https://stackoverflow.com/questions/5970595/how-to-create-a-device-node-from-the-init-module-code-of-a-linux-kernel-module
+https://stackoverflow.com/questions/5970595/how-to-create-a-device-node-from-the-init-module-code-of-a-linux-kernel-module/45531867#45531867
 */
 
 #include <linux/cdev.h>

kernel_module/pci.c

@@ -63,7 +63,7 @@ TODO: does it have any side effects? Set in the edu device at:
 
 ## Play with registers from the CLI
 
-Use setpci, devmem2 and /sys.
+Use setpci, devmem and /sys.
 */
 
 #include <asm/uaccess.h> /* put_user */

kernel_module/platform_device.c

@@ -12,7 +12,7 @@ Expected outcome after insmod:
 
 Also without insmodding this module, try:
 
-	devmem2 0x101e9000 w 0x12345678
+	devmem 0x101e9000 w 0x12345678
 
 which touches from userland through /dev/mem.
 */

kernel_module/user/devmem3.c

@@ -1,106 +0,0 @@
-/*
-Adapted from: http://free-electrons.com/pub/mirror/devmem2.c
-
-Forked because of the unpredictable access widths:
-https://bugs.busybox.net/show_bug.cgi?id=10171
-*/
-
-#include <ctype.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <signal.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/mman.h>
-#include <sys/types.h>
-#include <termios.h>
-#include <unistd.h>
-
-#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
-  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
-
-int main(int argc, char **argv) {
-	int access_type = 'w';
-	unsigned long map_size, map_mask;
-	off_t target;
-	uintmax_t read_result, writeval;
-    int fd;
-    void *map_base, *virt_addr;
-
-    map_size = sysconf(_SC_PAGE_SIZE);
-    map_mask = map_size - 1;
-	if(argc < 2) {
-		fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
-			"\taddress : memory address to act upon\n"
-			"\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
-			"\tdata    : data to be written\n\n",
-			argv[0]);
-		exit(1);
-	}
-	target = strtoul(argv[1], 0, 0);
-
-	if(argc > 2)
-		access_type = tolower(argv[2][0]);
-
-
-    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
-    printf("/dev/mem opened.\n");
-    fflush(stdout);
-
-    /* Map one page */
-    map_base = mmap(0, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~map_mask);
-    if(map_base == (void *) -1) FATAL;
-    printf("Memory mapped at address %p.\n", map_base);
-    fflush(stdout);
-
-    virt_addr = map_base + (target & map_mask);
-    switch(access_type) {
-		case 'b':
-			read_result = *((uint8_t *) virt_addr);
-			break;
-		case 'h':
-			read_result = *((uint16_t *) virt_addr);
-			break;
-		case 'w':
-			read_result = *((uint32_t *) virt_addr);
-			break;
-		case 'q':
-			read_result = *((uint64_t *) virt_addr);
-			break;
-		default:
-			fprintf(stderr, "Illegal data type '%c'.\n", access_type);
-			exit(2);
-	}
-    printf("Value at address 0x%jX (%p): 0x%jX\n", (uintmax_t)target, virt_addr, (uintmax_t)read_result);
-    fflush(stdout);
-
-	if(argc > 3) {
-		writeval = strtoul(argv[3], 0, 0);
-		switch(access_type) {
-			case 'b':
-				*((uint8_t *) virt_addr) = writeval;
-				read_result = *((uint8_t *) virt_addr);
-				break;
-			case 'h':
-				*((uint16_t *) virt_addr) = writeval;
-				read_result = *((uint16_t *) virt_addr);
-				break;
-			case 'w':
-				*((uint32_t *) virt_addr) = writeval;
-				read_result = *((uint32_t *) virt_addr);
-				break;
-			case 'q':
-				*((uint64_t *) virt_addr) = writeval;
-				read_result = *((uint64_t *) virt_addr);
-				break;
-		}
-		printf("Written 0x%jX; readback 0x%jX\n", (uintmax_t)writeval, (uintmax_t)read_result);
-		fflush(stdout);
-	}
-
-	if(munmap(map_base, map_size) == -1) FATAL;
-    close(fd);
-    return 0;
-}

kernel_module/user/usermem.c

@@ -48,7 +48,7 @@ see: https://stackoverflow.com/questions/11891979/how-to-access-mmaped-dev-mem-w
 
 Then:
 
-	devmem2 0x7c7b800
+	devmem 0x7c7b800
 
 Possible output:
 
@@ -60,7 +60,7 @@ to our physical address and given to the process that mapped /dev/mem.
 
 And finally, let's change the value!
 
-	devmem2 0x7c7b800 w 0x9abcdef0
+	devmem 0x7c7b800 w 0x9abcdef0
 
 After one second, we see on the screen:
 

rootfs_overlay/uio_read.sh

@@ -8,8 +8,8 @@ echo '1234 11e9' > /sys/bus/pci/drivers/uio_pci_generic/new_id
 insmod /irq.ko
 base="$(setpci -d 1234:11e9 BASE_ADDRESS_0)"
 # Start generating interrupt.
-/devmem3.out "0x${base}" w 0x12345678
+devmem "0x${base}" w 0x12345678
 # Stop generating interrupt.
-/devmem3.out "0x$(($base + 4))" w 0x12345678
+devmem "0x$(($base + 4))" w 0x12345678
-/devmem3.out "0x${base}" w 0x12345678
+devmem "0x${base}" w 0x12345678
-/devmem3.out "0x$(($base + 4))" w 0x12345678
+devmem "0x$(($base + 4))" w 0x12345678

rootfs_overlay/virt_to_phys.sh

@@ -6,11 +6,11 @@ cat lkmc_virt_to_phys
 # k = 0x12345678
 # i = 0x12345678
 addr=$(awk '$1 == "virt_to_phys_k" { print $2 }' lkmc_virt_to_phys)
-devmem2 "$addr"
+devmem "$addr"
-devmem2 "$addr" w 0x9ABCDEF0
+devmem "$addr" w 0x9ABCDEF0
 addr=$(awk '$1 == "virt_to_phys_i" { print $2 }' lkmc_virt_to_phys)
-devmem2 "$addr"
+devmem "$addr"
-devmem2 "$addr" w 0x9ABCDEF0
+devmem "$addr" w 0x9ABCDEF0
 cat lkmc_virt_to_phys
 # k = 0x9ABCDEF0
 # i = 0x12345678