Date: Fri, 08 Apr 2005 11:58:14 -0700 From: Julian Elischer <julian@elischer.org> To: FreeBSD Current <freebsd-current@freebsd.org> Subject: odd bus_dma_tag_create(...maxsegsize..) . question for some devices.. Message-ID: <4256D446.4090009@elischer.org>
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The man page specifies: for the maxsegsz parameter:
--------
maxsegsz
Maximum size, in bytes, of a segment in any DMA
mapped region associated with dmat.
----------
some devices seem to use the highest address in the buffer here...
it seems wrong..
anyone know if these devices need this, or their maxsegsiz and maxsize
values should be 1 greater?
Most devices use BUS_SPACE_MAXSIZE_24BIT or BUS_SPACE_MAXSIZE_32BIT
which are defined as odd values (not even) as well (see below, at end).
Probably this is where the misunderstanding came from.
the (bad?) examples
an/if_an_pci.c- 0x3ffff, /*
maxsize XXX */
an/if_an_pci.c- 1, /*
nsegments */
an/if_an_pci.c- 0xffff, /*
maxsegsize XXX */
I'm guessing this should be 0x10000 and 0x 10000 (nsegs = 1).
./sound/usb/uaudio_pcm.c- /*maxsize*/
bufsz,
./sound/usb/uaudio_pcm.c- /*nsegments*/ 1,
./sound/usb/uaudio_pcm.c- /*maxsegz*/
0x3fff,
I'm guessing these should be 0x1000 , 4, 0x4000 (depending possibly on
the USB adapter used.)
./ubsec/ubsec.c- 0x3ffff,
/* maxsize */
./ubsec/ubsec.c- UBS_MAX_SCATTER,
/* nsegments */
./ubsec/ubsec.c- 0xffff,
/* maxsegsize */
I think this should be:
0x40000, UBS_MAX_SCATTER, 0x10000
but I dont know the hardware.
i386/include/bus_at386.h:#define BUS_SPACE_MAXSIZE_24BIT 0xFFFFFF
i386/include/bus_pc98.h:#define BUS_SPACE_MAXSIZE_24BIT 0xFFFFFF
i386/include/bus_at386.h:#define BUS_SPACE_MAXSIZE_32BIT 0xFFFFFFFF
i386/include/bus_pc98.h:#define BUS_SPACE_MAXSIZE_32BIT 0xFFFFFFFF
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