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Subject: UIO: uio_mem does not handle devices above 4 GB address
Date: Wed, 1 Apr 2009 13:20:49 -0400
Message-ID: <6FCCA913376DD7488F4139A4D11B8F48AC8CDE@troe2k1.cs.myharris.net>
Thread-Topic: UIO: uio_mem does not handle devices above 4 GB address
Thread-Index: Acmy7jNciFodbr1kQ4u5rd4/KXsL3A==
From: "Herrera-Bendezu, Luis" <lherrera@harris.com>
To: <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1315
Lines: 39

I am working on a PPC440EPx board with some FPGAs located at
addresses above 4 GB and kernel version 2.6.28.7. The UIO driver is
used to access the FPGAs. I get following error when trying to read
FPGA registers:
Machine check in kernel mode.
Data Read PLB Error

The problem is traced to member addr in struct uio_mem:
struct uio_mem {
    unsigned long     addr;
    unsigned long     size;
    int               memtype;
    void __iomem      *internal_addr;
    struct uio_map    *map;
};

When UIO_MEM_PHYS is used with device address > 32-bit then
uio_mmap_physical() remaps address using idev->info->mem[mi].addr
thus loosing high address bits.

One way to solve this problem is to change addr member to:
    phys_addr_t       addr;

and modify corresponding attributes in uio.c. Only concern is that
uio_vma_fault() calls virt_to_page() and vmalloc_to_page() where both
have addr arg (unsigned long) and (const void *) respectively for
powerpc. But these functions are only used for UIO_MEM_LOGICAL and
UIO_MEM_VIRTUAL.

Any alternative approach?

Thanks,
Luis

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