From owner-freebsd-hackers Thu Jun 3 11:43:12 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from uni4nn.gn.iaf.nl (osmium.gn.iaf.nl [193.67.144.12]) by hub.freebsd.org (Postfix) with ESMTP id 706DC159B5 for ; Thu, 3 Jun 1999 11:42:56 -0700 (PDT) (envelope-from wilko@yedi.iaf.nl) Received: from yedi.iaf.nl (uucp@localhost) by uni4nn.gn.iaf.nl (8.9.2/8.9.2) with UUCP id TAA20518; Thu, 3 Jun 1999 19:52:12 +0200 (MET DST) Received: (from wilko@localhost) by yedi.iaf.nl (8.9.3/8.9.3) id TAA00686; Thu, 3 Jun 1999 19:30:20 +0200 (CEST) (envelope-from wilko) From: Wilko Bulte Message-Id: <199906031730.TAA00686@yedi.iaf.nl> Subject: Re: The choice of MAXPHYS In-Reply-To: <19990603172907.A20792@hal.mpn.cp.philips.com> from Jos Backus at "Jun 3, 1999 5:29: 7 pm" To: Jos.Backus@nl.origin-it.com Date: Thu, 3 Jun 1999 19:30:20 +0200 (CEST) Cc: zzhang@cs.binghamton.edu, freebsd-hackers@FreeBSD.ORG X-Organisation: Private FreeBSD site - Arnhem, The Netherlands X-pgp-info: PGP public key at 'finger wilko@freefall.freebsd.org' X-Mailer: ELM [version 2.4ME+ PL43 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG As Jos Backus wrote ... > On Thu, Jun 03, 1999 at 10:40:10AM -0400, Zhihui Zhang wrote: > > The value of MAXPHYS is chosen to be 64K for the maximum raw I/O transfer > > size. I am wondering why it is not set larger. > > Just a guess: maybe this has something to do with DMA address counters on ISA > cards being 16 bit? (ducks) Or is this total nonsense? :-) 20 bits. But older cards can do no more than 64 kB. What would be nice to have is some kind of interface so that the card driver can tell the higher layers what it's capabilities are in this respect. | / o / / _ Arnhem, The Netherlands - Powered by FreeBSD - |/|/ / / /( (_) Bulte WWW : http://www.tcja.nl http://www.freebsd.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message