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Date: Fri, 28 Feb 2003 09:49:18 -0600
From: Eli Carter <eli.carter@inet.com>
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To: "Martin J. Bligh" <mbligh@aracnet.com>
CC: Jeff Garzik <jgarzik@pobox.com>, Andi Kleen <ak@suse.de>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Matthew Wilcox <willy@debian.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Proposal: Eliminate GFP_DMA
References: <20030228064631.G23865@parcelfarce.linux.theplanet.co.uk.suse.lists.linux.kernel> <p73heao7ph2.fsf@amdsimf.suse.de> <20030228141234.H23865@parcelfarce.linux.theplanet.co.uk> <1046445897.16599.60.camel@irongate.swansea.linux.org.uk> <20030228143405.I23865@parcelfarce.linux.theplanet.co.uk> <1046447737.16599.83.camel@irongate.swansea.linux.org.uk> <20030228145614.GA27798@wotan.suse.de> <20030228152502.GA32449@gtf.org> <10490000.1046446480@[10.10.2.4]>
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Martin J. Bligh wrote:
>>>>>umm.  are you volunteering to convert drivers/net/macmace.c to the pci_*
>>>>>API then?  also, GFP_DMA is used on, eg, s390 to get memory below 2GB and
>>>>>on ia64 to get memory below 4GB.
>>>>
>>>>The ia64 is a fine example of how broken it is. People have to hack around 
>>>>with GFP_DMA meaning different things on ia64 to everything else. It needs
>>>>to die. 
>>>
>>>At least on x86-64 it is still needed when you need have some hardware
>>>with address limits < 4GB (e.g. an 24bit soundcard)
>>>
>>>pci_* on K8 only allows address mask 0xffffffff or unlimited.
>>
>>That's a bit broken...  I have an ALS4000 PCI soundcard that is a 24-bit
>>soundcard.  pci_set_dma_mask should support 24-bits accordingly,
>>otherwise it's a bug in your platform implementation...  Nobody will be
>>able to use certain properly-written drivers on your platform otherwise.
> 
> 
> If we're going to really sort this out, would be nice to just pass an upper
> bound for an address to __alloc_pages, instead of a simple bitmask ;-)

To do it properly, I think you'd need to give a range, not just an upper 
bound.  On some ARM / XScale systems, you can specify a window of your 
RAM that is visible on the PCI bus.  That may be a case too odd to care 
about, but I'm going to have to at some point in the future....

Eli
--------------------. "If it ain't broke now,
Eli Carter           \                  it will be soon." -- crypto-gram
eli.carter(a)inet.com `-------------------------------------------------

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