From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.17.24]:63577 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755102AbaJGVj4 (ORCPT ); Tue, 7 Oct 2014 17:39:56 -0400 From: Arnd Bergmann To: Lorenzo Pieralisi Cc: Liviu Dudau , "linux-arm-kernel@lists.infradead.org" , Mark Rutland , "devicetree@vger.kernel.org" , "jason@lakedaemon.net" , "linux-doc@vger.kernel.org" , Marc Zyngier , "linux-pci@vger.kernel.org" , Will Deacon , "linux-kernel@vger.kernel.org" , "robh+dt@kernel.org" , "suravee.suthikulpanit@amd.com" , Catalin Marinas , "bhelgaas@google.com" , "tglx@linutronix.de" , "rmk+kernel@arm.linux.org.uk" Subject: Re: [RFC 2/4] PCI: generic: Add support for ARM64 and MSI(x) Date: Tue, 07 Oct 2014 23:39:47 +0200 Message-ID: <3978481.XNAIA6gzAG@wuerfel> In-Reply-To: <20141007144750.GB30590@e102568-lin.cambridge.arm.com> References: <1411937610-22125-1-git-send-email-suravee.suthikulpanit@amd.com> <3659934.boXsmm8jcn@wuerfel> <20141007144750.GB30590@e102568-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-pci-owner@vger.kernel.org List-ID: On Tuesday 07 October 2014 15:47:50 Lorenzo Pieralisi wrote: > On Tue, Oct 07, 2014 at 02:52:27PM +0100, Arnd Bergmann wrote: > > On Tuesday 07 October 2014 13:06:59 Lorenzo Pieralisi wrote: > > > On Wed, Oct 01, 2014 at 10:38:45AM +0100, Arnd Bergmann wrote: > > > > > > [...] > > > > > > > pci_mmap_page_range could either get generalized some more in an attempt > > > > to have a __weak default implementation that works on ARM, or it could > > > > be changed to lose the dependency on pci_sys_data instead. In either > > > > case, the change would involve using the generic pci_host_bridge_window > > > > list. > > > > > > On ARM pci_mmap_page_range requires pci_sys_data to retrieve its > > > mem_offset parameter. I had a look, and I do not understand *why* > > > it is required in that function, so I am asking. That function > > > is basically used to map PCI resources to userspace, IIUC, through > > > /proc or /sysfs file mappings. As far as I understand those mappings > > > expect VMA pgoff to be the CPU address when files representing resources > > > are mmapped from /proc and 0 when mmapped from /sys (I mean from > > > userspace, then VMA pgoff should be updated by the kernel to map the > > > resource). > > > > Applying the mem_offset is certainly the more intuitive way, since > > that lets you read the PCI BAR values from a device and access the > > device with the appropriate offsets. > > Ok, but I am referring to this snippet (drivers/pci/pci-sysfs.c): > > /* pci_mmap_page_range() expects the same kind of entry as coming > * from /proc/bus/pci/ which is a "user visible" value. If this is > * different from the resource itself, arch will do necessary fixup. > */ > pci_resource_to_user(pdev, i, res, &start, &end); > > --> Here start represents a CPU physical address, if pci_resource_to_user() > does not fix it up, correct ? > > vma->vm_pgoff += start >> PAGE_SHIFT; > > [...] > > return pci_mmap_page_range(...); > > pci_mmap_page_range() applies (mem_offset >> PAGE_SHIFT) to pgoff in the > ARM implemention. > > Is not there a mismatch here on platforms where mem_offset != 0 ? Yes, I think that's right: ARM never gained its own pci_resource_to_user() implementation, presumably because nobody ran into this problem and debugged it all the way. Arnd