Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759030AbYJXEvB (ORCPT ); Fri, 24 Oct 2008 00:51:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758724AbYJXEum (ORCPT ); Fri, 24 Oct 2008 00:50:42 -0400 Received: from rgminet01.oracle.com ([148.87.113.118]:55858 "EHLO rgminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758204AbYJXEuj (ORCPT ); Fri, 24 Oct 2008 00:50:39 -0400 Date: Thu, 23 Oct 2008 21:49:48 -0700 From: Randy Dunlap To: Keith Packard Cc: Ingo Molnar , Jesse Barnes , Nick Piggin , Dave Airlie , Yinghai Lu , Linux Kernel Mailing List Subject: Re: [PATCH] Add io-mapping functions to dynamically map large device apertures Message-Id: <20081023214948.0c248345.randy.dunlap@oracle.com> In-Reply-To: <1224746087-13991-2-git-send-email-keithp@keithp.com> References: <20081022093615.GF12453@elte.hu> <1224746087-13991-1-git-send-email-keithp@keithp.com> <1224746087-13991-2-git-send-email-keithp@keithp.com> Organization: Oracle Linux Eng. X-Mailer: Sylpheed 2.5.0 (GTK+ 2.12.0; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAQAAAAI= X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4669 Lines: 131 On Thu, 23 Oct 2008 00:14:46 -0700 Keith Packard wrote: > Documentation/io-mapping.txt | 84 ++++++++++++++++++++++++++++ > include/linux/io-mapping.h | 125 ++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 209 insertions(+), 0 deletions(-) > create mode 100644 Documentation/io-mapping.txt > create mode 100644 include/linux/io-mapping.h > > diff --git a/Documentation/io-mapping.txt b/Documentation/io-mapping.txt > new file mode 100644 > index 0000000..ebf6dc5 > --- /dev/null > +++ b/Documentation/io-mapping.txt > @@ -0,0 +1,84 @@ > +The io_mapping functions in linux/io.h provide an abstraction for io-mapping.h ? > +efficiently mapping small regions of an io device to the CPU. The initial IO or I/O, please > +usage is to support the large graphics aperture on 32-bit processors where > +ioremap_wc cannot be used to statically map the entire aperture to the CPU > +as it would consume too much of the kernel address space. > + > +A mapping object is created during driver initialization using > + > + struct io_mapping * > + io_mapping_create_wc(unsigned long base, unsigned long size) > + > + 'base' is the bus address of the region to be made > + mappable, while 'size' indicates how large a mapping region to > + enable. Both are in bytes. > + > + This _wc variant provides a mapping which may only be used > + with the io_mapping_map_atomic_wc or io_mapping_map_wc. > + > +With this mapping object, individual pages can be mapped either atomically > +or not, depending on the necessary scheduling environment. Of course, atomic > +maps are more efficient: > + > + void * > + io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset) > + > + 'offset' is the offset within the defined mapping region. > + Accessing addresses beyond the region specified in the > + creation function yields undefined results. Using an offset > + which is not page aligned yields an undefined result. The > + return value points to a single page in CPU address space. > + > + This _wc variant returns a write-combining map to the > + page and may only be used with with ... > + > + Note that the task may not sleep while holding this page > + mapped. > + > + void > + io_mapping_unmap_atomic(void *vaddr) > + > + 'vaddr' must be the the value returned by the last > + io_mapping_map_atomic_wc call. This unmaps the specified > + page, and allows the task to sleep once again. s/,// > + > +If you need to sleep while holding the lock, you can use the non-atomic > +variant, although they may be significantly slower; s/;/./ > + > + void * > + io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset) > + > + This works like io_mapping_map_atomic_wc except it allows > + the task to sleep while holding the page mapped. > + > + void > + io_mapping_unmap(void *vaddr) > + > + This works like io_mapping_unmap_atomic, except it is used > + for pages mapped with io_mapping_map_wc. > + > +At driver close time, the io_mapping object must be freed: > + > + void > + io_mapping_free(struct io_mapping *mapping) > + > +Current Implementation: > + > +The initial implementation of these functions use existing mapping uses > +mechanisms and so provide only an abstraction layer and no new provides > +functionality. > + > +On 64-bit processors, io_mapping_create_wc calls ioremap_wc for the whole > +range, creating a permanent kernel-visible mapping to the resource. The > +map_atomic and map functions add the requested offset to the base of the > +virtual address returned by ioremap_wc. > + > +On 32-bit processors with HIGHMEM defined, io_mapping_map_atomic_wc uses > +kmap_atomic_pfn to map the specified page in an atomic fashion; > +kmap_atomic_pfn isn't really supposed to be used with device pages, but it > +provides an efficient mapping for this usage. > + > +On 32-bit processors without HIGHMEM defined, io_mapping_map_atomic_wc and > +io_mapping_map_wc both use ioremap_wc, a terribly inefficient function which > +performs an IPI to inform all processors about the new mapping. This results > +in a significant performance penalty. And I wish you could lose that horrible (non-Linux kernel) style of function return type on a separate line. --- ~Randy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/