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    SubjectRe: Linux 2.5.44-ac1
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    On Tue, 2002-10-22 at 13:27, Alan Cox wrote:
    > ** I strongly recommend saying N to IDE TCQ options otherwise this
    > should hopefully build and run happily.

    I don't have the IDE TCQ options on and am still having an issue with a
    kernel oops in the default kernel code. I did some digging after I
    noticed it in 2.5.43 and found a possibility for a null pointer in the
    code within the ide_iomio_dma function in ide-dma.c The problem shows
    itself if you only enable the secondary channel of your IDE controller.
    I understand this is a strange set up, but it could happen in a machine
    that boots off of SCSI and uses IDE disks for DATA or a CD Burner. I
    came up with a fix, some extra sanity checks before this line in the
    code:

    hwif->dma_master = (hwif->channel) ? hwif->mate->dma_base : base;

    Because it is the hwif->mate variable that is null when it gets here and
    if hwif->channel is not 0 I am taking it from the logic on this line
    that hwif->mate should not be a null variable. So I applied the sainity
    checks in the attached patch and this seems to work. I did this against
    the 2.5.43 and 2.5.44 kernels, and have posted patches for each of them
    but no one seems interested. If I am completely off base here, just let
    me know and I'll go back to the code and look for a different way to
    conquer this little bug.

    Jason




    diff -u -r linux-2.5.44-vanilla/drivers/ide/ide-dma.c linux-2.5.44/drivers/ide/ide-dma.c
    --- linux-2.5.44-vanilla/drivers/ide/ide-dma.c 2002-10-21 08:02:49.000000000 -0500
    +++ linux-2.5.44/drivers/ide/ide-dma.c 2002-10-21 08:56:49.000000000 -0500
    @@ -905,7 +905,12 @@
    request_region(base+16, hwif->cds->extra, hwif->cds->name);
    hwif->dma_extra = hwif->cds->extra;
    }
    - hwif->dma_master = (hwif->channel) ? hwif->mate->dma_base : base;
    + if(!hwif->mate && hwif->channel){
    + hwif->dma_master=base;
    + }
    + else{
    + hwif->dma_master = (hwif->channel) ? hwif->mate->dma_base : base;
    + }
    if (hwif->dma_base2) {
    if (!check_mem_region(hwif->dma_base2, ports))
    request_mem_region(hwif->dma_base2, ports, hwif->name);
    @@ -925,8 +930,13 @@
    if ((hwif->cds->extra) && (hwif->channel == 0)) {
    request_region(base+16, hwif->cds->extra, hwif->cds->name);
    hwif->dma_extra = hwif->cds->extra;
    + }
    + if(!hwif->mate && hwif->channel){
    + hwif->dma_master=base;
    + }
    + else{
    + hwif->dma_master = (hwif->channel) ? hwif->mate->dma_base : base;
    }
    - hwif->dma_master = (hwif->channel) ? hwif->mate->dma_base : base;
    if (hwif->dma_base2) {
    if (!request_region(hwif->dma_base2, ports, hwif->name))
    {
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