Date:	Thu, 30 Aug 2012 23:03:04 +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>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: RE: Using uio_pdrv to create an platform device for an FPGA, mmap()
 fails

 >[Added Greg Kroah-Hartman to Cc:]
>
>On Thu, Aug 30, 2012 at 08:10:11PM +0000, Worth, Kevin wrote:
>> >> 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,
>
>That doesn't matter. If it helps YOU that the code is maintained in mainline,
>post it.
>
>>  but the code seems like
>> possibly useful sample/example code.
>
>That is another good argument.

Perhaps this could be genericized to be a generic "Memory Map Userspace
IO Device" that takes a base address and a length in config (since those
are really the only things that are particular to my device/usage).
Could be enhanced to allow for additional maps, etc. or just serve as a
working example. Docs could then also simply refer to this as an example
of a device that uses the uio_pdrv driver.

>
>> Perhaps patching the HOWTO like
>> http://www.kernel.org/doc/htmldocs/uio-howto.html#uio_pci_generic_example
>> is the right approach?
>
>Oh, if you could hack up a patch for the documentation, that would be great.
>But please make it a second patch, don't mix it with your driver code.

Certainly these would belong in separate patches.

>
>Thanks,
>Hans
>
>> 
>> >
>> >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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