Messages in this thread | | | Date | Thu, 13 Mar 2008 15:53:58 -0600 | From | "Grant Likely" <> | Subject | Re: Linux UIO driver cache problem in PowerPC (fix) |
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On Thu, Mar 13, 2008 at 1:19 AM, Hans-Jürgen Koch <hjk@linutronix.de> wrote: > Am Wed, 12 Mar 2008 15:22:59 -0400 > schrieb "Jean-Samuel Chenard" <jsamch@gmail.com>: > > > 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. > > > > ==== > > 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 <linux/string.h> > > #include <linux/kobject.h> > > #include <linux/uio_driver.h> > > +#include <asm/pgtable.h> > > > > #define UIO_MAX_DEVICES 255 > > > > @@ -447,6 +448,8 @@ static int uio_mmap_physical(struct > > vm_area_struct *vma) > > > > vma->vm_flags |= VM_IO | VM_RESERVED; > > > > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > > + > > return remap_pfn_range(vma, > > vma->vm_start, > > idev->info->mem[mi].addr >> PAGE_SHIFT, > > ==== > > > > 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 > >
-- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- 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/
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