Date: Fri, 7 Jan 2000 09:46:41 -0800 (PST) From: Matthew Jacob <mjacob@feral.com> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: De la Cruz Lugo Eric <eric@iteso.mx>, freebsd-alpha@FreeBSD.ORG, sos@FreeBSD.ORG Subject: Re: HARDWARE.TXT specific for Alpha? Message-ID: <Pine.BSF.4.10.10001070941310.8867-100000@beppo.feral.com> In-Reply-To: <14454.1900.901358.626546@grasshopper.cs.duke.edu>
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> The problem is that we need to be able to DMA to/from any address is > RAM. On most platforms, the default direct-mapped DMA window is 1GB > in size, so we cannot exceed 1GB. It is possible to alter the number, > size & placement of such windows so as to increase the amount of RAM > one can DMA to/from. I have done this for the 21264s which is why > they can have 2GB. > > Another solution would be to set up temporary scatter/gather dma > mappings for all DMA & not just ISA DMA. This would alow memory sizes > greater than 4GB. This would require changes to many device drivers > and all drivers would need to support this mechanism to be able to use > it. I don't see this happening any time soon. It's easy to enforce this, btw- just remove the alpha_XXX_dmamap so that drivers have to use the busdma map routines instead of the compatibility define of vtophys. This is why I mentioned this to Soren about the so-called 'new' ATA driver (for which he got unbelievingly annoying in return about). This isn't going to happen any time soon as a default- there are too many drivers even in NetBSD which is more stringent about this than FreeBSD that still depend on this. However, we'll probably do something like add an option that says "use large memory" that will force the issue. -matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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