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Date: Fri, 4 Mar 2016 10:27:17 +0100 From: Tomasz Nowicki <tn@...ihalf.com> To: Bjorn Helgaas <helgaas@...nel.org> Cc: arnd@...db.de, will.deacon@....com, catalin.marinas@....com, rafael@...nel.org, hanjun.guo@...aro.org, Lorenzo.Pieralisi@....com, okaya@...eaurora.org, jiang.liu@...ux.intel.com, jchandra@...adcom.com, Stefano.Stabellini@...citrix.com, robert.richter@...iumnetworks.com, mw@...ihalf.com, Liviu.Dudau@....com, ddaney@...iumnetworks.com, wangyijing@...wei.com, Suravee.Suthikulpanit@....com, msalter@...hat.com, linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org, jcm@...hat.com Subject: Re: [PATCH V5 01/15] ACPI: MCFG: Move mmcfg_list management to drivers/acpi Hi Bjorn, On 03.03.2016 23:51, Bjorn Helgaas wrote: > Hi Tomasz, Jayachandran, et al, > > On Tue, Feb 16, 2016 at 02:53:31PM +0100, Tomasz Nowicki wrote: >> From: Jayachandran C <jchandra@...adcom.com> >> >> Move pci_mmcfg_list handling to a drivers/acpi/pci_mcfg.c. This is >> to share the API and code with ARM64 later. The corresponding >> declarations are moved from asm/pci_x86.h to linux/pci-acpi.h >> >> As a part of this we introduce three functions that can be >> implemented by the arch code: pci_mmconfig_map_resource() to map a >> mcfg entry, pci_mmconfig_unmap_resource to do the corresponding >> unmap and pci_mmconfig_enabled to see if the arch setup of >> mcfg entries was successful. We also provide weak implementations >> of these, which will be used from ARM64. On x86, we retain the >> old logic by providing platform specific implementation. >> >> This patch is purely rearranging code, it should not have any >> impact on the logic of MCFG parsing or list handling. > > I definitely want to figure out how to make this work well on ARM64. > I need to ponder this some more, so these are just some initial > thoughts. > > My first impression is that (a) the x86 MCFG code is an unmitigated > disaster, and (b) we're trying a little too hard to make that mess > generic. I think we might be better served if we came up with some > cleaner, more generic code that we can use for ARM64 today, and > migrate x86 toward that over time. > > My concern is that if we elevate the current x86 code to be > "arch-independent", we will be perpetuating some interfaces and > designs that shouldn't be allowed to escape arch/x86. > > Some of the code that moved to drivers/acpi/pci_mcfg.c is not really > ACPI-specific, and could potentially be used for non-ACPI bridges that > support ECAM. I'd like to see that sort of code moved to a new file > like drivers/pci/ecam.c. Actually I split it as you suggested in the previous patch set. Please have a look at: https://lkml.org/lkml/2016/2/4/646 Especially patches [0-6] which handle MMCONFIG refactoring. Thanks, Tomasz
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