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: Fri, 27 Mar 2015 21:30:29 +0100 Message-ID: <20150327203029.GM5622__28031.5379881815$1427488392$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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Ybatm-00023J-Ao for xen-devel@lists.xenproject.org; Fri, 27 Mar 2015 20:30:34 +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 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? Luis