Date: Wed, 31 Oct 2007 13:26:39 +0100
From: Jens Axboe <jens.axboe@oracle.com>
To: Jeff Garzik <jeff@garzik.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Daniel Drake <dsd@gentoo.org>,
       linux list <linux-kernel@vger.kernel.org>, linux-ide@vger.kernel.org
Subject: Re: "Fix ATAPI transfer lengths" causes CD writing regression
Message-ID: <20071031122639.GN5059@kernel.dk>
References: <47274A5F.6070409@gentoo.org> <20071030153417.59b9182c@the-village.bc.nu> <47276DCA.1000808@gentoo.org> <20071030190153.373c9347@the-village.bc.nu> <47278439.4030801@gentoo.org> <20071031114958.210bd7cc@the-village.bc.nu> <20071031115754.GK5059@kernel.dk> <472872F6.70802@garzik.org>
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On Wed, Oct 31 2007, Jeff Garzik wrote:
> 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.

Right, that's of course problematic... There has to be a way to recover
that situation though, or you can't export any user command issue
facility.

-- 
Jens Axboe

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