From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755872AbYJWHPt (ORCPT ); Thu, 23 Oct 2008 03:15:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752990AbYJWHP2 (ORCPT ); Thu, 23 Oct 2008 03:15:28 -0400 Received: from home.keithp.com ([63.227.221.253]:47703 "EHLO keithp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752708AbYJWHP1 (ORCPT ); Thu, 23 Oct 2008 03:15:27 -0400 From: Keith Packard To: Ingo Molnar Cc: Jesse Barnes , Nick Piggin , Dave Airlie , Yinghai Lu , Linux Kernel Mailing List , Keith Packard Subject: [PATCH] Add io-mapping functions to dynamically map large device apertures Date: Thu, 23 Oct 2008 00:14:46 -0700 Message-Id: <1224746087-13991-2-git-send-email-keithp@keithp.com> X-Mailer: git-send-email 1.5.6.5 In-Reply-To: <1224746087-13991-1-git-send-email-keithp@keithp.com> References: <20081022093615.GF12453@elte.hu> <1224746087-13991-1-git-send-email-keithp@keithp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Graphics devices have large PCI apertures which would consume a significant fraction of a 32-bit address space if mapped during driver initialization. Using ioremap at runtime is impractical as it is too slow. This new set of interfaces uses atomic mappings on 32-bit processors and a large static mapping on 64-bit processors to provide reasonable 32-bit performance and optimal 64-bit performance. The current implementation sits atop the existing CONFIG_HIGHMEM kmap_atomic mechanism for 32-bit processors when present. When absent, it just uses ioremap, which remains horribly inefficient. Fixing non-HIGHMEM 32-bit kernels to provide per-CPU mappings ala HIGHMEM would resolve that performance issue. Signed-off-by: Keith Packard --- 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 +efficiently mapping small regions of an io device to the CPU. The initial +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 + + 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. + +If you need to sleep while holding the lock, you can use the non-atomic +variant, although they may be significantly slower; + + 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 +mechanisms and so provide only an abstraction layer and no new +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. diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h new file mode 100644 index 0000000..dcc24d5 --- /dev/null +++ b/include/linux/io-mapping.h @@ -0,0 +1,125 @@ +/* + * Copyright © 2008 Keith Packard + * + * This file is free software; you can redistribute it and/or modify + * it under the terms of version 2 of the GNU General Public License + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. + */ + +#ifndef _LINUX_IO_MAPPING_H +#define _LINUX_IO_MAPPING_H + +#include +#include +#include +#include + +/* + * The io_mapping mechanism provides an abstraction for mapping + * individual pages from an io device to the CPU in an efficient fashion. + * + * See Documentation/io_mapping.txt + */ + +/* this struct isn't actually defined anywhere */ +struct io_mapping; + +#ifdef CONFIG_X86_64 + +/* Create the io_mapping object*/ +static inline struct io_mapping * +io_mapping_create_wc(unsigned long base, unsigned long size) +{ + return (struct io_mapping *) ioremap_wc(base, size); +} + +static inline void +io_mapping_free(struct io_mapping *mapping) +{ + iounmap(mapping); +} + +/* Atomic map/unmap */ +static inline void * +io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset) +{ + return ((char *) mapping) + offset; +} + +static inline void +io_mapping_unmap_atomic(void *vaddr) +{ +} + +/* Non-atomic map/unmap */ +static inline void * +io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset) +{ + return ((char *) mapping) + offset; +} + +static inline void +io_mapping_unmap(void *vaddr) +{ +} + +#endif /* CONFIG_X86_64 */ + +#ifdef CONFIG_X86_32 +static inline struct io_mapping * +io_mapping_create_wc(unsigned long base, unsigned long size) +{ + return (struct io_mapping *) base; +} + +static inline void +io_mapping_free(struct io_mapping *mapping) +{ +} + +/* Atomic map/unmap */ +static inline void * +io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset) +{ + offset += (unsigned long) mapping; +#ifdef CONFIG_HIGHMEM + return kmap_atomic_pfn(offset >> PAGE_SHIFT, KM_USER0); +#else + return ioremap_wc(offset, PAGE_SIZE); +#endif +} + +static inline void +io_mapping_unmap_atomic(void *vaddr) +{ +#ifdef CONFIG_HIGHMEM + kunmap_atomic(vaddr, KM_USER0); +#else + iounmap(vaddr); +#endif +} + +static inline void * +io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset) +{ + offset += (unsigned long) mapping; + return ioremap_wc(offset, PAGE_SIZE); +} + +static inline void +io_mapping_unmap(void *vaddr) +{ + iounmap(vaddr); +} +#endif /* CONFIG_X86_32 */ + +#endif /* _LINUX_IO_MAPPING_H */ -- 1.5.6.5