From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [BUILD FAILURE 01/04] Next June 04:PPC64 randconfig [drivers/staging/comedi/drivers.o] Date: Tue, 09 Jun 2009 13:50:18 +1000 Message-ID: <1244519418.5235.2.camel@pasglop> References: <20090605182625.24093.7808.sendpatchset@elm3a191.beaverton.ibm.com> <1244261806.31984.36.camel@pasglop> <20090606055103.GA9446@kroah.com> <200906060936.22322.fmhess@speakeasy.net> <1244385405.5265.7.camel@subratamodak.linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:58215 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997AbZFIDvK (ORCPT ); Mon, 8 Jun 2009 23:51:10 -0400 In-Reply-To: <1244385405.5265.7.camel@subratamodak.linux.ibm.com> Sender: linux-next-owner@vger.kernel.org List-ID: To: subrata@linux.vnet.ibm.com Cc: fmhess@users.sourceforge.net, Greg KH , Ian Abbott , David Miller , sachinp@linux.vnet.ibm.com, sfr@canb.auug.org.au, linux-kernel@vger.kernel.org, Linuxppc-dev@ozlabs.org, linux-next@vger.kernel.org, paulus@samba.org, Geert.Uytterhoeven@sonycom.com, geert@linux-m68k.org On Sun, 2009-06-07 at 20:06 +0530, Subrata Modak wrote: > On Sat, 2009-06-06 at 09:36 -0400, Frank Mori Hess wrote: > > On Saturday 06 June 2009, Greg KH wrote: > > > Frank and Ian, any thoughts about the vmap call in the > > > comedi_buf_alloc() call? Why is it using PAGE_KERNEL_NOCACHE, and what > > > is the prealloc_buf buffer used for? > > > > It is a circular buffer used to hold data streaming either to or from a > > board (for example when producing an analog output waveform). Reads and > > writes to the device files read/write to the circular buffer, plus a few > > drivers do dma directly to/from it. I personally don't have a problem > > with requiring drivers to have their own dma buffers and making them copy > > data between their private dma buffers and the main circular buffer. I > > guess the original design wanted to support zero-copy dma. > > Great to hear that. How about a patch that solves my build problem on > PPC64(the problem seems to be existing for long) ? In any case, doing PAGE_KERNEL_NOCACHE for DMA memory is incorrect on many architectures. So at this stage, there's no much option but ifdef I suspect for now until this is fixed properly. It does make sense to want to have some memory like that shared between user space and DMA, though I don't know what the right approach that works on all archs is at this stage. Worth asking the Alsa guys, I think they have similar issues :-) But doing double buffering might do the trick fine for now. Cheers, Ben.