Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751297AbVIPVYV (ORCPT ); Fri, 16 Sep 2005 17:24:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751299AbVIPVYV (ORCPT ); Fri, 16 Sep 2005 17:24:21 -0400 Received: from kepler.fjfi.cvut.cz ([147.32.6.11]:57762 "EHLO kepler.fjfi.cvut.cz") by vger.kernel.org with ESMTP id S1751297AbVIPVYV (ORCPT ); Fri, 16 Sep 2005 17:24:21 -0400 Date: Fri, 16 Sep 2005 23:24:08 +0200 (CEST) From: Martin Drab To: Arjan van de Ven cc: Linux Kernel Mailing List Subject: Re: mmap(2)ping of pci_alloc_consistent() allocated buffers on 2.4 kernels question/help In-Reply-To: <1126896652.3103.10.camel@localhost.localdomain> Message-ID: References: <1126896652.3103.10.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2166 Lines: 59 On Fri, 16 Sep 2005, Arjan van de Ven wrote: > On Fri, 2005-09-16 at 20:33 +0200, Martin Drab wrote: > > Hi, > > > > can anyone explain me why it is not possible to mmap(2) a buffer > > allocated in kernel by pci_alloc_consistent() to userspace on a 2.4 > > kernel? > > > > In kernel PCI device initialization function I do something like: > > > > ... > > kladdr = pci_alloc_consistent (dev, BUFSIZE, &baddr); > > ... > > > > Then I send the physical address (i.e. the value of phaddr = __pa(kladdr)) > > to the userspace application, and then when in the userspace I do > > something like > > > > ... > > fd = fopen ("/dev/mem", O_RDWR); > > buf = mmap (NULL, BUFSIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, phaddr); > > ... > > > yuch. > why don't you make your device have an mmap operation instead? > (the device node that you use to get your physical address to userspace > in the first place) And would that help anyhow? Just a background: This is a RT driver for the RT Linux (that's why the 2.4 kernel). It is a data acquisition card. What I would like to do is: Driver allocates a finite (predefined) number of DMA buffers with pci_alloc_consistent() during the initialization. (This fixed alloc is necessary, since when you switch the driver into RT you cannot do any memory allocations anymore). And then I would like to fill a buffer via DMA, send a notice to the app. via the RT FIFO device that a buffer is filled, app. then calls the ioctl of the RT FIFO with the buffer number (obtained via the RT FIFO) that he wants to mmap, the ioctl mmaps it to the app., app. uses the data, and then calls another ioctl to unmap the buffer and release it for next filling. There's just a limited way to communicate between the RT and non-RT part of the kernel/app. The RT-FIFOs and their IOCTLs are safe. I'm not entirely sure a simple mmap would be safe here, but I may try that. Martin - 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/