From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753090AbbC0Uag (ORCPT ); Fri, 27 Mar 2015 16:30:36 -0400 Received: from cantor2.suse.de ([195.135.220.15]:58755 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752957AbbC0Uad (ORCPT ); Fri, 27 Mar 2015 16:30:33 -0400 Date: Fri, 27 Mar 2015 21:30:29 +0100 From: "Luis R. Rodriguez" To: Andy Lutomirski Cc: Bjorn Helgaas , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Mauro Carvalho Chehab , Mike Marciniszyn , "Luis R. Rodriguez" , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Juergen Gross , Jan Beulich , Borislav Petkov , Suresh Siddha , venkatesh.pallipadi@intel.com, Dave Airlie , "linux-kernel@vger.kernel.org" , Linux Fbdev development list , X86 ML , "xen-devel@lists.xenproject.org" , Ingo Molnar , Daniel Vetter , Antonino Daplas , Jean-Christophe Plagniol-Villard , Tomi Valkeinen Subject: Re: [PATCH v1 06/47] mtrr: add __arch_phys_wc_add() Message-ID: <20150327203029.GM5622@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-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Luis R. Rodriguez" Date: Fri, 27 Mar 2015 20:30:29 +0000 Subject: Re: [PATCH v1 06/47] mtrr: add __arch_phys_wc_add() Message-Id: <20150327203029.GM5622@wotan.suse.de> List-Id: 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> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andy Lutomirski Cc: Bjorn Helgaas , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , Mauro Carvalho Chehab , Mike Marciniszyn , "Luis R. Rodriguez" , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Juergen Gross , Jan Beulich , Borislav Petkov , Suresh Siddha , venkatesh.pallipadi@intel.com, Dave Airlie , "linux-kernel@vger.kernel.org" , Linux Fbdev development list , X86 ML , "xen-devel@lists.xenproject.org" , Ingo Molnar , Daniel Vetter , Antonino Daplas , Jean-Christophe Plagniol-Villard , Tomi Valkeinen 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