From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Luis R. Rodriguez" Subject: Re: [PATCH v1 06/47] mtrr: add __arch_phys_wc_add() Date: Sat, 28 Mar 2015 00:04:40 +0100 Message-ID: <20150327230440.GO5622__28646.2065684193$1427497622$gmane$org@wotan.suse.de> References: <1426893517-2511-1-git-send-email-mcgrof@do-not-panic.com> <1426893517-2511-7-git-send-email-mcgrof@do-not-panic.com> <20150327195350.GJ5622@wotan.suse.de> <20150327203029.GM5622@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YbdJ2-0002jx-6W for xen-devel@lists.xenproject.org; Fri, 27 Mar 2015 23:04:48 +0000 Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andy Lutomirski Cc: Linux Fbdev development list , Daniel Vetter , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Jan Beulich , "H. Peter Anvin" , Suresh Siddha , Tomi Valkeinen , X86 ML , Ingo Molnar , Dave Airlie , Ingo Molnar , Borislav Petkov , Jean-Christophe Plagniol-Villard , Antonino Daplas , Mauro Carvalho Chehab , Mike Marciniszyn , "xen-devel@lists.xenproject.org" , Bjorn Helgaas , Thomas Gleixner , Juergen Gross , "Luis R. Rodriguez" , linux-kernel@vger.k List-Id: xen-devel@lists.xenproject.org On Fri, Mar 27, 2015 at 02:23:16PM -0700, Andy Lutomirski wrote: > On Fri, Mar 27, 2015 at 1:30 PM, Luis R. Rodriguez wrote: > > On Fri, Mar 27, 2015 at 12:58:02PM -0700, Andy Lutomirski wrote: > >> On Fri, Mar 27, 2015 at 12:53 PM, Luis R. Rodriguez wrote: > >> > On Fri, Mar 20, 2015 at 04:48:46PM -0700, Andy Lutomirski wrote: > >> >> On Fri, Mar 20, 2015 at 4:17 PM, Luis R. Rodriguez > >> >> wrote: > >> >> > From: "Luis R. Rodriguez" > >> >> > > >> >> > Ideally on systems using PAT we can expect a swift > >> >> > transition away from MTRR. There can be a few exceptions > >> >> > to this, one is where device drivers are known to exist > >> >> > on PATs with errata, another situation is observed on > >> >> > old device drivers where devices had combined MMIO > >> >> > register access with whatever area they typically > >> >> > later wanted to end up using MTRR for on the same > >> >> > PCI BAR. This situation can still be addressed by > >> >> > splitting up ioremap'd PCI BAR into two ioremap'd > >> >> > calls, one for MMIO registers, and another for whatever > >> >> > is desirable for write-combining -- in order to > >> >> > accomplish this though quite a bit of driver > >> >> > restructuring is required. > >> >> > > >> >> > Device drivers which are known to require large > >> >> > amount of re-work in order to split ioremap'd areas > >> >> > can use __arch_phys_wc_add() to avoid regressions > >> >> > when PAT is enabled. > >> >> > > >> >> > For a good example driver where things are neatly > >> >> > split up on a PCI BAR refer the infiniband qib > >> >> > driver. For a good example of a driver where good > >> >> > amount of work is required refer to the infiniband > >> >> > ipath driver. > >> >> > > >> >> > This is *only* a transitive API -- and as such no new > >> >> > drivers are ever expected to use this. > >> >> > >> >> What's the exact layout that this helps? I'm sceptical that this can > >> >> ever be correct. > >> >> > >> >> Is there some awful driver that has a large ioremap that's supposed to > >> >> contain multiple different memtypes? > >> > > >> > Yes, I cc'd you just now on one where I made changes on a driver which uses one > >> > PCI with mixed memtypes and uses MTRR to hole in WC. A transition to > >> > arch_phys_wc_add() is therefore not possible if PAT is enabled as it would > >> > regress those drivers by making the MTRR WC hole trick non functional. > >> > The changes are non trivial and so in this series I supplied changes on > >> > one driver only to show the effort required. The other drivers which > >> > required this were: > >> > > >> > Driver File > >> > ------------------------------------------------------------ > >> > fusion drivers/message/fusion/mptbase.c > >> > ivtv drivers/media/pci/ivtv/ivtvfb.c > >> > ipath drivers/infiniband/hw/ipath/ipath_driver.c > >> > > >> > This series makes those drivers use __arch_phys_wc_add() more as a > >> > transitory phase in hopes we can address the proper split as with the > >> > atyfb illustrates. For ipath the changes required have a nice template > >> > with the qib driver as they share very similar driver structure, the > >> > qib driver *did* do the nice split. > >> > > >> >> If so, can we ioremap + set_page_xyz instead? > >> > > >> > I'm not sure I see which call we'd use. Care to provide an example patch > >> > alternative for the atyfb as a case in point alternative to the work required > >> > to do the split? > >> > > >> > >> I'm still confused. Would it be insufficient to ioremap_nocache the > >> whole thing and then call set_memory_wc on parts of it? (Sorry, > >> set_page_xyz was a typo.) > > > > I think that would be a sexy alternative. > > > > In this driver's case the thing is a bit messy as it not only used > > the WC MTRR for a hole but it also then used a UC MTRR on top of > > it all, so since I already tried to address the split, and if we address > > the power of 2 woes, I think it'd be best to try to remove the UC MTRR > > and just avoid set_page_wc() in this driver's case, but for the other cases > > (fusion, ivtv, ipath) I think this makes sense. > > > > Thoughts? > > Once that WC MTRR is in place, I think you really need UC and not UC- > if you want to override it. Otherwise I agree with all of this. Do you mean that the UC MTRR work around that was in place might not have really been effective? Not quite sure what you mean. I don't think I follow. Luis