From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id 1CC9BB6F34 for ; Wed, 10 Jun 2009 04:54:59 +1000 (EST) MIME-Version: 1.0 Sender: geert.uytterhoeven@gmail.com In-Reply-To: <1244572446.5497.32.camel@subratamodak.linux.ibm.com> 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> <1244519418.5235.2.camel@pasglop> <1244572446.5497.32.camel@subratamodak.linux.ibm.com> Date: Tue, 9 Jun 2009 20:54:54 +0200 Message-ID: <10f740e80906091154p60babd99t8452696ec7ccc8f3@mail.gmail.com> Subject: Re: [BUILD FAILURE 01/04] Next June 04:PPC64 randconfig [drivers/staging/comedi/drivers.o] From: Geert Uytterhoeven To: subrata@linux.vnet.ibm.com Content-Type: text/plain; charset=UTF-8 Cc: sachinp@linux.vnet.ibm.com, fmhess@users.sourceforge.net, sfr@canb.auug.org.au, linux-kernel@vger.kernel.org, Linuxppc-dev@ozlabs.org, Ian Abbott , linux-next@vger.kernel.org, paulus@samba.org, Greg KH , Geert.Uytterhoeven@sonycom.com, David Miller List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Jun 9, 2009 at 20:34, Subrata Modak wro= te: > On Tue, 2009-06-09 at 13:50 +1000, Benjamin Herrenschmidt wrote: >> 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? =C2=A0Why 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 fro= m a >> > > board (for example when producing an analog output waveform). =C2=A0= Reads and >> > > writes to the device files read/write to the circular buffer, plus a= few >> > > drivers do dma directly to/from it. =C2=A0I 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.= =C2=A0I >> > > 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. > > Ok. But, i am not sure whether Greg will agree to this. If, Ok, is the > following patch i sent earlier Ok ? > > http://lkml.org/lkml/2009/6/5/462, Your patch helps powerpc only. Compilation is still broken on most other architectures. >> 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. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k= .org In personal conversations with technical people, I call myself a hacker. Bu= t when I'm talking to journalists I just say "programmer" or something like t= hat. -- Linus Torvalds