Messages in this thread | | | Subject | Re: [PATCH] ALSA: hda-intel - Disable MSI support by default | From | Benjamin Herrenschmidt <> | Date | Wed, 15 Nov 2006 18:23:40 +1100 |
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On Tue, 2006-11-14 at 20:07 -0800, David Miller wrote: > From: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Date: Wed, 15 Nov 2006 15:01:00 +1100 > > > Out of curiosity. Are you sure there is no case of stupid bridge > > converting the MSI into some APIC/whatever interrupt for the CPU > > potentially before all previous DMA have been fully pushed to the > > coherent domain (still in some internal store queue for example) ? > > That would really suck, wouldn't it :) > > However, they have to do all the work of processing the memory > transation that the MSI is on the PCI bus, I don't think they would go > so far out of their way to reorder things even if they converted the > MSI packet into a PIN to the APIC, for example.
That would suck and not surprise me that much in fact... Take the Apple bridge... it's unclear at which point they actually decode the MSI and HT interrupts (the later are just internally converted to MSI-like stores) to turn them into toggling of MPIC lines, but it probably happens as an MMIO slave on the main xbar and I'm not 100% certain it provides ordering vs. the previous stores to memory as they are in the coherent domain and the MMIO is not. I just hope very much :-) Because the store queue to memory can re-order on U4.
Ben.
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