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    SubjectRe: ISP1760 driver crashes
    On Wed, Nov 19 2008, Alan Stern wrote:
    > On Wed, 19 Nov 2008, Sebastian Andrzej Siewior wrote:
    >
    > > Hommel, Thomas (GE EntSol, Intelligent Platforms) wrote:
    > >
    > > > I indeed have HIGHMEM enabled in my configuration.
    > > > I recompiled the kernel without HIGHMEM and it works. I don't think that
    > > > this a satisfying solution for a board with up to 2GB of RAM and
    > > > considerable amount of VMALLOC space, but at least this works.
    > > > If you have any more ideas how to circumvent this, please let me know.
    > > Sure, this is not a sollution but atleast now I know what happens:
    > > - The kernel allocates memory for transfer
    > > - the memory is highmem and not in kernel so the buffer is NULL
    > > - we don't have a dma-mask and therefore the dma address is 0
    > > - boom
    > >
    > > The sollution would be probably to prevent the usb-storage core to
    > > allocate memory from HIGHMEM.
    >
    > usb-storage doesn't allocate the memory. The memory is allocated by
    > the block layer or the filesystem.
    >
    > > Now I don't if there is a flag for something
    > > like that and I am not using that. On the other hand this may be broken
    > > for a long time and you are the first one which has that much memory with
    > > no DMA-capable USB controller.
    >
    > Jens, is there any way to tell the kernel that a device uses PIO and
    > therefore its buffers shouldn't be allocated in high memory? For
    > example, shouldn't a NULL dma_mask do this?

    Sure, just use blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH), then you are
    certain that you will always have a virtual mapping for the IO you
    receive.

    Or you can use the bio kmap/kunmap helpers to get such a mapping
    temporarily if you wish. But if your pio condition is permanent, you may
    as well just use bouncing.

    --
    Jens Axboe



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