devmem3

buildroot_config_fragment

@@ -70,3 +70,32 @@ BR2_PACKAGE_HOST_DTC=y
 # 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.
+#
+# Read is possible from Linux with:
+#
+#     hexdump /sys/bus/pci/devices/0000:00:05.0/config
+#
+# but setpci provies nice human readable register names, e.g.:
+#
+#     setpci --dumpregs
+#
+# then and then get the values with either bus or device id:
+#
+#     setpci -s 0000:00:05.0 BASE_ADDRESS_0
+#     setpci -d 1234:11e9 BASE_ADDRESS_0
+#
+# Note however that BASE_ADDRESS_0 also appears when you do:
+#
+#     lspci -v
+#
+# Then you can try messing with that address with:
+#
+#     devmem2 0xfeb52000 w 0x12345678
+#
+# which for our pci_min device fires interrupts.
+#
+BR2_PACKAGE_PCIUTILS=y

kernel_config_fragment

@@ -138,11 +138,12 @@ CONFIG_ARM64_PTDUMP=y
 
 ## UIO
 
-# Userspace drivers.
+# Userspace drivers: allow you to handle IRQs and do memory IO from userland through a /dev file.
 #
 # Superseded by the more featureful VFIO.
 #
-# Documentation/DocBook/uio-howto.tmpl
+# Documentation/DocBook/uio-howto.tmpl contains actual userland examples
+# for the generic examples under drivers/uio
 #
 # UIO interface in a nutshell:
 #

kernel_module/user/devmem3.c

@@ -0,0 +1,103 @@
+/*
+Adapted from: http://free-electrons.com/pub/mirror/devmem2.c
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <ctype.h>
+#include <termios.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <stdint.h>
+  
+#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
+  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
+ 
+#define MAP_SIZE 4096UL
+#define MAP_MASK (MAP_SIZE - 1)
+
+int main(int argc, char **argv) {
+    int fd;
+    void *map_base, *virt_addr; 
+	uintmax_t read_result, writeval;
+	off_t target;
+	int access_type = 'w';
+	
+	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%X; readback 0x%jX\n", (unsigned int)writeval, (unsigned int)read_result); 
+		fflush(stdout);
+	}
+	
+	if(munmap(map_base, MAP_SIZE) == -1) FATAL;
+    close(fd);
+    return 0;
+}

kernel_module/user/uio_read.c

@@ -1,9 +1,15 @@
 /*
 Adapted from: https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
 
-    modprobe uio_pdrv_genirq
+    modprobe uio_pci_generic
+    echo '1234 11e9' > /sys/bus/pci/drivers/uio_pci_generic/new_id
+    /uio_read.out &
 
-TODO get working.
+TODO get working. The problem now is how to generate IRQs to test our IRQ handling:
+
+-   a synchronous IRQ needs regwrites to be kicked off, but mmap does not seem to work with this driver
+-   a custom PCI periodic timer device would also need to be initiazed by some regwrite, otherwise
+    early interrupts before the OS is setup would crash everything?
 
 Handle interrupts from userland and print a message to stdout.
 */
@@ -17,17 +23,31 @@ Handle interrupts from userland and print a message to stdout.
 #include <sys/types.h>
 #include <unistd.h> /* write */
 
+#include <assert.h>
+#include <sys/mman.h>
+
 int main(int argc, char **argv)
 {
 
-    char *dev;
+    char *dev = "/dev/uio0";
-    if (argc < 2) {
+    if (argc > 1) {
+        dev = argv[1];
+        exit(EXIT_FAILURE);
     }
-    int fd = open("/dev/uio", O_RDWR);
+    int fd = open(dev, O_RDWR);
     if (fd < 0) {
         perror("open");
         exit(EXIT_FAILURE);
     }
+
+    /* TODO not supported by this kernel module? */
+	/*int *addr = mmap(NULL, sysconf(_SC_PAGE_SIZE), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);*/
+	/*if (addr == MAP_FAILED) {*/
+		/*perror("mmap");*/
+		/*assert(0);*/
+	/*}*/
+	/**addr = 0x12345678;*/
+
     while (1) {
         uint32_t info = 1;
         size_t nb = write(fd, &info, sizeof(info));