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    SubjectRe: Bug: Latest (rc2 and beyond) kernel fails on Dreamcast
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    On Tue, 2009-01-20 at 20:40 +0000, Adrian McMenamin wrote:
    > 2009/1/20 Paul Mundt <lethal@linux-sh.org>:
    > > On Mon, Jan 19, 2009 at 10:33:57PM +0000, Adrian McMenamin wrote:
    > >> 2009/1/19 Adrian McMenamin <lkmladrian@gmail.com>:
    > >> > I haven't had time to look at this, but the most up to date kernel
    > >> > (and the one of around a week ago also) fails to boot, seemingly
    > >> > seeking an IP address for the 8139too based NIC.
    > >>
    > >> > [ 4.664236] Sending DHCP requests .<3>eth0: PCI Bus error 2200.
    > >> > [ 4.669582] eth0: PCI Bus error 2200.
    > >>
    > >> And the bisection reveals the following:
    > >>
    > >> adrian@bossclass:~/linux-2.6$ git bisect bad
    > >> 58c6d3dfe436eb8cfb451981d8fdc9044eaf42da is first bad commit
    > >> commit 58c6d3dfe436eb8cfb451981d8fdc9044eaf42da
    > >> Author: Johannes Weiner <hannes@cmpxchg.org>
    > >> Date: Tue Jan 6 14:43:10 2009 -0800
    > >>
    > >> dma-coherent: catch oversized requests to dma_alloc_from_coherent()
    > >>
    >
    >
    >
    > >
    > > The dreamcast uses a 32kB coherent area for PCI DMA, which all of the
    > > 8139too allocations should fit under just fine. What does
    > > dma_alloc_from_coherent() say the requested size is, vs the per-device
    > > memory size for each allocation?
    > >
    >
    > Hmmm...
    >
    > >From printks I stuck in the code
    >
    > [ 3.641267] Size is 0x1800, mem->size is 0x8
    > [ 3.644996] Size is 0x2810, mem->size is 0x8
    >
    > The sizes are correct - the first is the TX buffer, the second RX, but
    > I have no idea why mem->size is set so low, I assume that is a bug
    > somewhere else in the Dreamcast code. Any clues gratefully received.
    > --


    Actually, it looks to me that the patch was wrong.

    This is from kernel/dma-coherent.c

    dev->dma_mem->size = pages;

    Yet this is the test applied in dma_alloc_from_coherent:

    if (unlikely(size > mem->size))

    Should surely be:

    if (unlikely (size > (mem->size >> PAGE_SHIFT)))

    Will patch that and try it




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