From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liviu Dudau Subject: Re: [PATCH v5 2/4] arm64: dts: APM X-Gene PCIe device tree nodes Date: Tue, 22 Apr 2014 13:49:37 +0100 Message-ID: <20140422124937.GE865@e106497-lin.cambridge.arm.com> References: <1395270762-6055-1-git-send-email-tinamdar@apm.com> <1395270762-6055-3-git-send-email-tinamdar@apm.com> <20140416170545.GD4858@bart> <20140416212104.GA3469@obsidianresearch.com> <20140417002041.GE4858@bart> <20140417012434.GA8734@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20140417012434.GA8734@obsidianresearch.com> Content-Disposition: inline Sender: linux-pci-owner@vger.kernel.org To: Jason Gunthorpe Cc: Rob Herring , Tanmay Inamdar , Bjorn Helgaas , Arnd Bergmann , "grant.likely@linaro.org" , Rob Herring , Catalin Marinas , Rob Landley , "linux-pci@vger.kernel.org" , "devicetree@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "patches@apm.com" , "jcm@redhat.com" List-Id: devicetree@vger.kernel.org On Thu, Apr 17, 2014 at 02:24:34AM +0100, Jason Gunthorpe wrote: > On Thu, Apr 17, 2014 at 01:20:42AM +0100, Liviu Dudau wrote: >=20 > > > No spec says you can put config space into the ranges at all, nob= ody > > > should be doing that today, obviously some cases were missed duri= ng > > > review.. > >=20 > > ePAPR documents allows that when ss =3D=3D 00. >=20 > Which do you mean? The 'PCI Bus Binding' spec has fairly specific > language on how ranges should be used and interpreted, and it > precludes doing anything meaningful with config space (like requiring > b,d,f and r to be zeroed when doing compares against ranges, requirin= g > the ranges to represent the bridge windows, etc). >=20 > There is certainly room to invent something (like ECAM mapping) but > nothing is specified in that document. On more carefull reading of the Power_ePAPR_APPROVED_v1.0.pdf document that I have I agree, there is no meaningful way of describing one's config ranges. >=20 > The ePAPR document I have doesn't talk about PCI.. >=20 > If you've found a document that defines how it works then that change= s > things.. ;) >=20 > > > The comment about ECAM was intended as a general guidance on what > > > config space in ranges could/should be used for. > > >=20 > > > Right now config space shouldn't propagate out side any driver, s= o you > > > can probably just filter it in your generic code, and make it ver= y hard > > > and obviously wrong for a driver to parse ranges for config space= , so > > > we don't get more usages. > >=20 > > OK, this goes slightly against your email from 26th March: > >=20 > > "When we talked about this earlier on the DT bindings list the > > consensus seemed to be that configuration MMIO ranges should only b= e > > used if the underlying memory was exactly ECAM, and was not to be u= sed > > for random configuration related register blocks. > >=20 > > The rational being that generic code, upon seeing that ranges entry= , > > could just go ahead and assume ECAM mapping." > >=20 > > What I'm saying is that the only code that will see this ranges ent= ry will > > be the parsing code as if we try to create a resource out of the ra= nge > > and add it to the host bridge structure (not driver) we will confus= e the > > rest of the pci_host_bridge API. So we cannot do any ECAM accesses = (yet?). >=20 > Sorry if this seems unclear, what you quoted was from a specification > standpoint - someday defining config space ranges to be the ECAM > window makes the most sense. This is from the direction of precluding > drivers from using it for random purposes. >=20 > From a Linux standpoint, there is simply no infrastructure for generi= c > config access outside the driver, so config space must remain > contained in the driver, and shouldn't leak into the host bridge or > other core structures. >=20 > I think the shared code you are working on should simply ignore confi= g > ss ranges entirely, they have no defined meaning.. Agree. Less things to code for is always better! Best regards, Liviu >=20 > Regards, > Jason >=20 --=20 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D | I would like to | | fix the world, | | but they're not | | giving me the | \ source code! / --------------- =C2=AF\_(=E3=83=84)_/=C2=AF