linux-kernel - Using uio_pdrv to create an platform device for an FPGA, mmap() fails

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Date:	Wed, 29 Aug 2012 23:19:00 +0000
From:	"Worth, Kevin" <kevin.worth@...com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"Worth, Kevin" <kevin.worth@...com>
Subject: Using uio_pdrv to create an platform device for an FPGA, mmap()
 fails

I have below what appears to be a mostly-functional device using the UIO Platform Driver. The /sys entries I'd expect appear,  /proc/iomem contains " d0000000-d0000fff : myfpga", and lsuio sees the properties that I've set. However an mmap() from userspace (either my test program below or lsuio) fails. So close! (at least it would seem)

Finding a good example for this did not come easily (which is why I'm hitting LKML, since I know it'll get a lot of eyeballs and be archived). Maybe there was something obvious I missed, but the only "official" documentation I could locate was http://www.kernel.org/doc/htmldocs/uio-howto.html#using_uio_pdrv , and most everything else was snippets from presentations, papers, and forums that lacked completeness.

Thanks for the help any might be able to offer.
Please CC me on replies as I'm not ready to drink from the fire hose that is an LKML subscription.

# lsuio -v -m
uio0: name=uio_myfpga, version=0.1, events=0
        map[0]: addr=0xD0000000, size=4096, mmap test: FAILED
        Device attributes:
        uevent=DRIVER=uio_pdrv
        modalias=platform:uio_pdrv

------Kernelspace portion-------

#include <linux/platform_device.h>
#include <linux/uio_driver.h>
#include <linux/module.h>

#define MYFPGA_BASE     0xd0000000 // 3G
#define MYFPGA_SIZE     0x00040000 // 256k

static struct resource myfpga_resources[] = {
        {
                .start  = MYFPGA_BASE,
                .end    = MYFPGA_BASE + MYFPGA_SIZE - 1,
                .name   = "myfpga",
                .flags  = IORESOURCE_MEM
        }
};

static struct uio_info myfpga_uio_info = {
   .name = "uio_myfpga",
   .version = "0.1",
   .irq = UIO_IRQ_CUSTOM,
   .mem = {
        {
            .name = "myfpga",
            .memtype = UIO_MEM_PHYS,
            .addr = MYFPGA_BASE,
            .size = MYFPGA_SIZE
        }
    }
};

static struct platform_device_info myfpga_uio_pdevinfo = {
    .name = "uio_pdrv",
    .id = -1,
    .res = myfpga_resources,
    .num_res = 1,
    .data = &myfpga_uio_info,
    .size_data = sizeof(struct uio_info)
};

static struct platform_device *myfpga_uio_pdev;

static int __init myfpga_init(void)
{
    myfpga_uio_pdev = platform_device_register_full(&myfpga_uio_pdevinfo);
    if (IS_ERR(myfpga_uio_pdev)) {
        return PTR_ERR(myfpga_uio_pdev);
    }

    return 0;
}

static void __exit myfpga_exit(void)
{
    platform_device_unregister(myfpga_uio_pdev);
}

module_init(myfpga_init);
module_exit(myfpga_exit);

------Userspace portion-------

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <dirent.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define MYFPGA_BASE     0xd0000000 // 3G
#define MYFPGA_SIZE     0x00040000 // 256k
#define MYFPGA_UIO_NUM  0          // uio0

int main (int argc, char *argv[])
{
    int fd;
    void *iomem;
    fd = open("/dev/uio0", O_RDWR|O_SYNC);
    if (fd < 0) {
        printf("failed to open /dev/uio0, quitting\n");
        return -1;
    }
    /* Note offset has a special meaning with uio devices */
    iomem = mmap(NULL, MYFPGA_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd,
                 MYFPGA_UIO_NUM * getpagesize());
    if (iomem == MAP_FAILED) {
        printf("mmap failed, quitting\n");
        close(fd);
        return -2;
    }
    printf("mmap successful!\n");
    munmap(iomem, MYFPGA_SIZE);
    close(fd);
    return 0;
}
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