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    SubjectRe: "Fix ATAPI transfer lengths" causes CD writing regression
    Jens Axboe wrote:
    > On Wed, Oct 31 2007, Alan Cox wrote:
    >> On Tue, 30 Oct 2007 19:21:29 +0000
    >> Daniel Drake <dsd@gentoo.org> wrote:
    >>
    >>> Alan Cox wrote:
    >>>> I would guess Brasero is issuing a command with the length of data
    >>>> wrongly set. In the old code that might well just produce errors of the
    >>>> "Umm wtf is this data left over for ?", with the new code the drive is
    >>>> likely to change state as it knows the transfer size and that will
    >>>> *correctly* cause an HSM error and what follows.
    >>>>
    >>>> Now the question is who gets the length wrong - Brasero or the ata
    >>>> translation code in libata
    >>> Brasero does exactly the same as my test app which I attached to my last
    >>> mail. Is my test app wrong?
    >> Would need to double check the SCSI specificatons to be sure but I think
    >> you are asking for less data than the drive wishes to provide. You
    >> aren't allowed to do that with ATA.
    >
    > ide-cd handles this by throwing the excess away, which I think is the
    > sane way to do this.

    That's easy for the PIO case. But CD writing is normally DMA, which
    means you will get a DMA engine exception if the device wants to give
    you more data than the scatter/gather entries permit.

    Jeff



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