[7124] in linux-scsi channel archive
Re: scsi driver transfer size and sync mode
daemon@ATHENA.MIT.EDU (Kurt Garloff)
Fri Sep 3 04:11:24 1999
Date: Fri, 3 Sep 1999 09:32:00 +0200
From: Kurt Garloff <garloff@suse.de>
To: Tony Chung <chungto@ampex.com>
Cc: Doug Ledford <dledford@redhat.com>, linux-scsi@vger.rutgers.edu
Mail-Followup-To: Tony Chung <chungto@ampex.com>,
Doug Ledford <dledford@redhat.com>, linux-scsi@vger.rutgers.edu
In-Reply-To: <37CEFEDF.1EA8536@ampex.com>; from Tony Chung on Thu, Sep 02, 1999 at 03:49:04PM -0700
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On Thu, Sep 02, 1999 at 03:49:04PM -0700, Tony Chung wrote:
> Now I may be a little worry about what will happened when direct DMA to
> user space is supported in the future.
> I think currently the st driver is capable to allocate 1024K contingous
> physical memory
> (through special kernel funciton) but in the case of a user space, the
> malloc() will not be
> able to map to a contingous physcial memory. Again this is speaking from
> my experience=20
> from Solaris 7 and other Unices. There must be a reason for the folks at
> Sun Microsystem
> to change their page size from 8k (in Sparc platform) to 4k for x86
> platform.=20
As the PCI devices see memory bus adresses, which are more or less physical
addresses (shifted on some platforms), you need to have physically contigous
buffers for every SG segment. Probably you need to have the kernel allocate
this for you via some mmap() mechanism.
The reason for the page sizes with Sparc and ix86 is hardware: That's the
way the MMUs of the CPUs are designed.
Regards,
--=20
Kurt Garloff <garloff@suse.de> Wuppertal, FRG
PGP2 key: See mail header, key servers Linux kernel development
SuSE GmbH, N=FCrnberg, FRG SCSI drivers: tmscsim(DC390), DC395
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