From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from stat1.steeleye.com ([65.114.3.130]:59343 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S261706AbUCVE4s (ORCPT ); Sun, 21 Mar 2004 23:56:48 -0500 Subject: Re: can device drivers return non-ram via vm_ops->nopage? From: James Bottomley In-Reply-To: <20040322044615.GC2045@holomorphy.com> References: <20040321222327.D26708@flint.arm.linux.org.uk> <405E1859.5030906@pobox.com> <20040321225117.F26708@flint.arm.linux.org.uk> <20040321234515.G26708@flint.arm.linux.org.uk> <20040322002349.GZ2045@holomorphy.com> <405E3387.1050505@pobox.com> <20040322034509.GB2045@holomorphy.com> <1079930497.2045.69.camel@mulgrave> <20040322044615.GC2045@holomorphy.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: 21 Mar 2004 23:56:40 -0500 Message-Id: <1079931403.5345.74.camel@mulgrave> Mime-Version: 1.0 To: William Lee Irwin III Cc: linux-arch@vger.kernel.org, Jeff Garzik , Russell King , Linus Torvalds , David Woodhouse , Christoph Hellwig , Andrew Morton , Andrea Arcangeli List-ID: On Sun, 2004-03-21 at 23:46, William Lee Irwin III wrote: > Okay, this is bad news for sound (and possibly some graphics) drivers > on PA-RISC, since this mapping of coherent areas into userspace is > exactly what they're trying to do for the device interfaces they > export to the user. > > Are you seeing breakage there, or are the drivers doing this > unused on PA-RISC? Well, our older sound drivers have never worked since ALSA (they hang off the GSC bus which ALSA doesn't have an abstraction for). Mostly we use serial console, and a HP specific thing called a STI framebuffer for video. The problems I describe only occur if you try to mmap coherent memory. mmaping streaming memory is fine. But, I would expect that any arch with a virtually indexed cache would have similar problems: there may be many address aliases in the cache and the DMA controller probably only knows about one of them. James