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

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Date:	Thu, 30 Aug 2012 20:10:11 +0000
From:	"Worth, Kevin" <kevin.worth@...com>
To:	"Hans J. Koch" <hjk@...sjkoch.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>
Subject: RE: Using uio_pdrv to create an platform device for an FPGA, mmap()
 fails

>> Thanks for the reply, Hans. Your question about opening /dev/uio0 O_RDWR
>> prompted me to check out how I was creating /dev/uio0 ... my system
>> isn't using udev, and I was accidentally creating it with major/minor
>> number 254/0 instead of the correct 253/0 (found by looking at
>> /proc/devices). Fixed that and the mmap() call started working.
>
>Good.
>
>> 
>> Verified that if /dev/uio0 has permissions 0644, root can open it O_RDWR
>> and mmap PROT_READ | PROT_WRITE using the below code and write to an
>> address within my memory map. Of course this contradicts the statement
>> "/dev/uioX is a read-only file" in the UIO howto.
>
>You're right. That wants to be fixed...
>
>> 
>> Including my updated, tested code for completeness.
>> Note I also cleaned up the device registration a little by
>> using a different platform_device_register_ call and removing fields
>> in the struct uio_info that get filled in by uio_pdrv automatically.
>
>If you want to have that included in the mainline, please choose a more
>descriptive name than "myfpga" and send a proper patch.

I wasn't sure about submitting as a patch since it's for a custom FPGA
that I don't expect the community will be using, but the code seems like
possibly useful sample/example code. Perhaps patching the HOWTO like
http://www.kernel.org/doc/htmldocs/uio-howto.html#uio_pci_generic_example
is the right approach?

>
>Thanks,
>Hans
>
>> 
>> -Kevin
>> 
>> # lsuio -m -v
>> uio0: name=uio_myfpga, version=0.1, events=0
>>         map[0]: addr=0xD0000000, size=262144, mmap test: OK
>>         Device attributes:
>>         uevent=DRIVER=uio_pdrv
>>         modalias=platform:uio_pdrv
>> 
>> ------Kernelspace------
>> #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",
>> };
>> 
>> static struct platform_device *myfpga_uio_pdev;
>> 
>> static int __init myfpga_init(void)
>> {
>>     myfpga_uio_pdev = platform_device_register_resndata (NULL,
>>                                                          "uio_pdrv",
>>                                                          -1,
>>                                                          myfpga_resources,
>>                                                          1,
>>                                                          &myfpga_uio_info,
>>                                                          sizeof(struct uio_info)
>>                                                         );
>>     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-------
>> #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>
>> #include <stdint.h>
>> 
>> #define MYFPGA_BASE     0xd0000000 // 3G
>> #define MYFPGA_SIZE     0x00040000 // 256k
>> #define MYFPGA_MAP_NUM  0 // First and only defined map
>> 
>> #define BIT32(n) (1 << (n))
>> 
>> /* Use mmap()'ped address "iomem", not physical MYFPGA address */
>> #define MYFPGA_REG(iomem) (volatile uint32_t*)(iomem + 0x8) // Third 32-bit reg
>> 
>> 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_MAP_NUM * getpagesize());
>>     if (iomem == MAP_FAILED) {
>>         printf("mmap failed, quitting\n");
>>         close(fd);
>>         return -2;
>>     }
>> 
>>     /* Set bit 5 of MYFPGA_REG register */
>>     *MYFPGA_REG(iomem) |= BIT32(5);
>> 
>>     munmap(iomem, MYFPGA_SIZE);
>>     close(fd);
>>     return 0;
>> }
>>  
>>  
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