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    SubjectRe: ISP1760 driver crashes
    On Wed, Nov 19 2008, Alan Stern wrote:
    > On Wed, 19 Nov 2008, Jens Axboe wrote:
    >
    > > 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.
    >
    > Thank you.
    >
    > Thomas, the blk_queue_bounce_limit() routine is called in
    > drivers/scsi/scsi_lib.c:__scsi_alloc_queue(). The value it passes is
    > computed by scsi_calculate_bounce_limit(), and in that routine
    > host_dev->dma_mask should be NULL (since isp1760-hcd sets the mask to
    > NULL). Therefore the bounce limit should be 0xffffffff.
    >
    > Now maybe this value isn't correct. You can try the patch below to see
    > if it helps. If it doesn't, add a printk in __scsi_alloc_queue() to
    > see what bounce limit value is getting used.
    >
    > Alan Stern
    >
    >
    >
    > Index: usb-2.6/drivers/scsi/scsi_lib.c
    > ===================================================================
    > --- usb-2.6.orig/drivers/scsi/scsi_lib.c
    > +++ usb-2.6/drivers/scsi/scsi_lib.c
    > @@ -1684,7 +1684,7 @@ static void scsi_request_fn(struct reque
    > u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
    > {
    > struct device *host_dev;
    > - u64 bounce_limit = 0xffffffff;
    > + u64 bounce_limit = BLK_BOUNCE_HIGH;
    >
    > if (shost->unchecked_isa_dma)
    > return BLK_BOUNCE_ISA;
    >

    The best solution is probably to either provide a "doesn't do highmem"
    in the scsi host template, or provide an appropriate DMA mask for the
    pci device to indicate it through that setting instead.

    --
    Jens Axboe



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