Messages in this thread | | | Subject | Re: Can Linux live without DMA zone? | From | Arjan van de Ven <> | Date | Thu, 02 Nov 2006 23:19:05 +0100 |
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On Thu, 2006-11-02 at 16:26 -0500, Phillip Susi wrote: > Arjan van de Ven wrote: > > that's for the 32 bit boundary. THe problem is that there are 31, 30, 28 > > and 26 bit devices as well, and those are in more trouble, and will > > eventually fall back to GFP_DMA (inside the x86 PCI code; the driver > > just uses the pci dma allocation routines) if they can't get suitable > > memory otherwise.... > > > > It's all nice in theory. But then there is the reality that not all > > devices are nice pci device that implement the entire spec;) > > > > Right, but doesn't the bounce/allocation routine take as a parameter the > limit that the device can handle? If the device can handle 28 bit > addresses, then the kernel should not limit it to only 24 bits.
you're right in theory, but the kernel only has a few pools of memory available, but not at every bit boundary. there is a 32 bit pool (GFP_DMA32) on some, a 30-ish bit pool (GFP_KERNEL) on others, and a 24 bit pool (GFP_DMA) with basically nothing inbetween.
-- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org
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