From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hugh Dickins Subject: Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy_mem regression Date: Fri, 6 Feb 2009 12:56:52 +0000 (GMT) Message-ID: References: <1233867944.4612.104.camel@pasglop> <200902051433.23294.jbarnes@virtuousgeek.org> <1233898836.4612.116.camel@pasglop> Mime-Version: 1.0 Return-path: In-Reply-To: <1233898836.4612.116.camel@pasglop> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Benjamin Herrenschmidt Cc: "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Jesse Barnes On Fri, 6 Feb 2009, Benjamin Herrenschmidt wrote: > On Thu, 2009-02-05 at 14:33 -0800, Jesse Barnes wrote: > > > One option there would be to provide the file but just use anonymous memory to > > back it. X will happily think it's messing with legacy VGA memory, but it > > shouldn't matter that it's not actually affecting hw. > > What about this (untested) patch ? > > powerpc/pci: mmap anonymous memory when legacy_mem doesn't exist > > The new legacy_mem file in sysfs is causing problems with X on machines > that don't support legacy memory access. The way I initially implemented > it, we would fail with -ENXIO when trying to mmap it, thus exposing to > X that we do support the API but there is no legacy memory. > > Unfortunately, X poor error handling is causing it to fail to start when > it gets this error. > > This implements a workaround hack that instead maps anonymous memory > instead (using shmem if VM_SHARED is set, just like /dev/zero does). > > Signed-off-by: Benjamin Herrenschmidt > --- Beautiful idea, works very nicely for me. Put a dummy in the baby's mouth to stop it crying. I still don't understand the point of this legacy_mem file at all, and why X should want to mmap it, if it works so well when it's thus divorced from reality. But I won't worry my pretty little head over it any further - please don't waste your time trying to explain it to me! Thanks, Hugh > > Index: linux-work/arch/powerpc/kernel/pci-common.c > =================================================================== > --- linux-work.orig/arch/powerpc/kernel/pci-common.c 2009-02-06 16:23:36.000000000 +1100 > +++ linux-work/arch/powerpc/kernel/pci-common.c 2009-02-06 16:30:32.000000000 +1100 > @@ -561,8 +561,21 @@ int pci_mmap_legacy_page_range(struct pc > (unsigned long long)(offset + size - 1)); > > if (mmap_state == pci_mmap_mem) { > - if ((offset + size) > hose->isa_mem_size) > - return -ENXIO; > + /* Hack alert ! > + * > + * Because X is lame and can fail starting if it gets an error trying > + * to mmap legacy_mem (instead of just moving on without legacy memory > + * access) we fake it here by giving it anonymous memory, effectively > + * behaving just like /dev/zero > + */ > + if ((offset + size) > hose->isa_mem_size) { > + printk(KERN_DEBUG > + "Process %s (pid:%d) mapped non-existing PCI legacy memory for 0%04x:%02x\n", > + current->comm, current->pid, pci_domain_nr(bus), bus->number); > + if (vma->vm_flags & VM_SHARED) > + return shmem_zero_setup(vma); > + return 0; > + } > offset += hose->isa_mem_phys; > } else { > unsigned long io_offset = (unsigned long)hose->io_base_virt - _IO_BASE;