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Date: Sun, 14 Jun 2009 01:21:57 -0500
From: "Rick C. Petty" <rick-freebsd2008@kiwi-computer.com>
To: Alexander Motin <mav@FreeBSD.org>
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Cc: freebsd-multimedia@freebsd.org
Subject: Re: snd_hda works on i386, fails on amd64 (RELENG_7)
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On Fri, Jun 05, 2009 at 11:30:20AM +0300, Alexander Motin wrote:

> Also you may try to change
> 	sc->support_64bit = HDA_FLAG_MATCH(gcap, HDAC_GCAP_64OK);
> line to
> 	sc->support_64bit = 0;
> , to strictly limit driver to 32bit addresses ignoring hardware
> capabilities.

Hmm, I looked at the place that queries support_64bit, in hdac_dma_alloc as
part of the lowaddr to the bus_dma_tag_create(9) call:

	lowaddr = (sc->support_64bit) ? BUS_SPACE_MAXADDR :
	    BUS_SPACE_MAXADDR_32BIT;
	...

On a whim, I tried manually setting lowaddr to BUS_SPACE_MAXADDR_24BIT and
it worked!  A binary search revealed that it breaks for me when
lowaddr > 0x7FFFFFFF ... perhaps a 32-bit overflow bug related to DMA?

Out of curiosity, how come this same test (for support_64bit) isn't needed
before the bus_dma_tag_create() in hdac_attach?

-- Rick C. Petty