From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hs-out-0708.google.com (hs-out-0708.google.com [64.233.178.241]) by ozlabs.org (Postfix) with ESMTP id E77BFDDE98 for ; Fri, 14 Mar 2008 08:54:02 +1100 (EST) Received: by hs-out-0708.google.com with SMTP id z77so3424237hsz.9 for ; Thu, 13 Mar 2008 14:54:00 -0700 (PDT) Message-ID: Date: Thu, 13 Mar 2008 15:53:58 -0600 From: "Grant Likely" Sender: glikely@secretlab.ca To: "=?ISO-8859-1?Q?Hans-J=FCrgen_Koch?=" , "Josh Boyer" , linuxppc-embedded@ozlabs.org Subject: Re: Linux UIO driver cache problem in PowerPC (fix) In-Reply-To: <20080313081932.4edee290@dilbert.local> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 References: <169c03cb0803121222h5fca9cdal5af873cd2a700f4d@mail.gmail.com> <20080313081932.4edee290@dilbert.local> Cc: Jean-Samuel Chenard , LKML , Greg KH List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Mar 13, 2008 at 1:19 AM, Hans-J=FCrgen Koch wro= te: > Am Wed, 12 Mar 2008 15:22:59 -0400 > schrieb "Jean-Samuel Chenard" : > > > Hi, > > Hi Jean-Samuel, > thanks for your report. Please CC LKML if you find bugs like this. I > also added Grant Likely (PPC Xilinx Virtex maintainer), as it seems to > be a platform specific problem. Hmmm. I'm not a memory handling expert so I don't know what's going on here. Josh, does this look like anything that would be ppc405 related? g. > > > > > Experimenting with your userspace I/O driver on a Xilinx FPGA (PowerPC > > 405), I was having problems when reading hardware device registers > > mapped on my platform using the user-space mmap() call. > > > > After some investigation (looking at the driver/char/mspec.c file), I > > found that preventing caching of the page in uio_mmap_physical fixed > > my issues with userspace mmap() reading messed-up values. > > Hm, we already mark the page with VM_IO. That's sufficient on x86 and > arm. I'm not sure whether this is a bug in PPC memory handling. Why do > they cache VM_IO pages? > > > > > This patch is against your initial commit of the UIO driver in the > > mainline kernel tree. > > > > =3D=3D=3D=3D > > diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c > > index 865f32b..36e1123 100644 > > --- a/drivers/uio/uio.c > > +++ b/drivers/uio/uio.c > > @@ -22,6 +22,7 @@ > > #include > > #include > > #include > > +#include > > > > #define UIO_MAX_DEVICES 255 > > > > @@ -447,6 +448,8 @@ static int uio_mmap_physical(struct > > vm_area_struct *vma) > > > > vma->vm_flags |=3D VM_IO | VM_RESERVED; > > > > + vma->vm_page_prot =3D pgprot_noncached(vma->vm_page_prot); > > + > > return remap_pfn_range(vma, > > vma->vm_start, > > idev->info->mem[mi].addr >> PAGE_SHIFT, > > =3D=3D=3D=3D > > > > I am a bit unsure if this will break something in any of your uses of > > the UIO driver (on other platforms than ppc), but it really fixes > > things for me. > > It should be OK, but unneccesary on other platforms. I have no > objections, but I fear in 6 months we'll see a patch removing that > line again because it's not needed... > > > Let me know if you need more details on what was > > happening on my platform before I added this statement. > > I'd like to hear the opinion of people really involved in PPC memory > handling. > > > > > Thanks for the great driver for user-space I/O, it will save me lots > > of time in my research. > > > > Regards, > > > > Jean-Samuel > > Thanks, > Hans > > --=20 Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd.