From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Hancock Subject: Re: [LKML] Re: USB transfer_buffer allocations on 64bit systems Date: Fri, 9 Apr 2010 16:11:52 -0600 Message-ID: References: <20100409202533.GA8983@phenom.dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Alan Stern Cc: Konrad Rzeszutek Wilk , Pedro Ribeiro , Daniel Mack , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Greg KH , alsa-devel@alsa-project.org, linux-usb@vger.kernel.org List-Id: alsa-devel@alsa-project.org On Fri, Apr 9, 2010 at 3:23 PM, Alan Stern = wrote: > On Fri, 9 Apr 2010, Konrad Rzeszutek Wilk wrote: > >> On Fri, Apr 09, 2010 at 03:34:06PM -0400, Alan Stern wrote: >> > On Fri, 9 Apr 2010, Pedro Ribeiro wrote: >> > >> > > > The DMA pointers do indeed look sane. I wanted to take a deepe= r look at >> > > > this and set up a 64bit system today. However, I fail to see t= he problem >> > > > here. Pedro, how much RAM does your machine have installed? >> > >> > > It has 4 GB. >> > >> > That means DMA mapping cannot be the cause of the problem. =A0:-( >> >> That isn't entirely true. The BIOS usually allocates a 256 MB ACPI/P= CI hole >> that is under the 4GB. >> >> So end up with 3.7 GB, then the 256MB hole, and then right above the= 4GB >> you the the remaining memory: 4.3GB. > > How can Pedro find out what physical addresses are in use on his > system? If you have 4GB of RAM then almost certainly you have memory located at addresses over 4GB. If you look at the e820 memory map printed at the start of dmesg on bootup and see entries with addresses of 100000000 or higher reported as usable, then this is the case.