Driver mmap support and behavior

[Thomas Nemeth <thomas.nemeth@xxxxxxxxxxx>]

    Hi !

    After reading the LDD3 book I made a driver that needs to make some
    datas accessible to userland via mmap. These datas are exported by
    an FPGA on physical memory 0x10000000-0x10010000.

    The code of the driver's mmap function is:

------8<---------------------------------------------------------------
static int device_mmap(struct file *filp, struct vm_area_struct *vma)
{
        unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
        unsigned long phys_addr = FPGA_IOMEM_BASE1 + offset;
        unsigned long phys_size = BASE1_BYTES_SIZE - offset;
        unsigned long virt_size = vma->vm_end - vma->vm_start;

        if (virt_size > phys_size)
        {
                PERROR("virtual size > physical size !\n");
                return -EINVAL; /*  spans too high */
        }

        vma->vm_flags |= VM_IO | VM_RESERVED;

        if (io_remap_page_range(vma,
                                vma->vm_start,
                                phys_addr,
                                virt_size,
                                vma->vm_page_prot) != 0)
        {
                PERROR("couldn't remap FPGA IO memory to you address 
space.\n");
                return -EAGAIN;
        }

        vma->vm_file = filp;
        vma->vm_ops  = &device_vm_ops;
        device_vm_open(vma);

        return 0;
}
------8<---------------------------------------------------------------

    I took the code from the book and lightly adapted it to my needs...

    The problem I run into is that I must call msync() from user space
    so that the datas are really written back to the FPGA, even with the
    VM_IO | VM_RESERVED flags.
    mmap() is called with the MAP_SHARED (and PROT_READ | PROT_WRITE).

    Is there anything I could do so that data is written in sync without
    the need to call msync() ? What did I miss ?

    Thanks to all.


Thomas.
-- 
Thomas Nemeth - Ingénieur d'Études en Informatique Industrielle
                Industrial Computing Software Designer
BETAtech - 15, rue Apollo, Z.A. de Montredon, 31240, L'Union.
05 34 30 40 00  /  05 34 30 40 09

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