From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752095AbbD3WBW (ORCPT ); Thu, 30 Apr 2015 18:01:22 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:59060 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750717AbbD3WBU (ORCPT ); Thu, 30 Apr 2015 18:01:20 -0400 Message-ID: <5542A628.8050705@infradead.org> Date: Thu, 30 Apr 2015 15:01:12 -0700 From: Randy Dunlap User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: "Luis R. Rodriguez" , mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, bp@suse.de, plagnioj@jcrosoft.com, tomi.valkeinen@ti.com, daniel.vetter@intel.com, airlied@linux.ie CC: dledford@redhat.com, awalls@md.metrocast.net, syrjala@sci.fi, luto@amacapital.net, mst@redhat.com, cocci@systeme.lip6.fr, linux-kernel@vger.kernel.org, "Luis R. Rodriguez" , Toshi Kani , Jonathan Corbet , Dave Hansen , Suresh Siddha , Juergen Gross , Daniel Vetter , Dave Airlie , Antonino Daplas , Mel Gorman , Vlastimil Babka , Davidlohr Bueso , linux-fbdev@vger.kernel.org Subject: Re: [PATCH v4 2/6] x86: document WC MTRR effects on PAT / non-PAT pages References: <1430343851-967-1-git-send-email-mcgrof@do-not-panic.com> <1430343851-967-3-git-send-email-mcgrof@do-not-panic.com> In-Reply-To: <1430343851-967-3-git-send-email-mcgrof@do-not-panic.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/29/15 14:44, Luis R. Rodriguez wrote: > From: "Luis R. Rodriguez" > > --- > Documentation/x86/mtrr.txt | 18 +++++++++++++++--- > Documentation/x86/pat.txt | 40 +++++++++++++++++++++++++++++++++++++++- > arch/x86/kernel/cpu/mtrr/main.c | 3 +++ > 3 files changed, 57 insertions(+), 4 deletions(-) > > diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt > index cf08c9f..7e183e3 100644 > --- a/Documentation/x86/pat.txt > +++ b/Documentation/x86/pat.txt > @@ -102,7 +104,43 @@ wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc() > as step 0 above and also track the usage of those pages and use set_memory_wb() > before the page is freed to free pool. > > - > +MTRR effects on PAT / non-PAT systems > +------------------------------------- > + > +The following table provides the effects of using write-combining MTRRs when > +using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally > +mtrr_add() usage will be phased in favor of arch_phys_wc_add() which will > +be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add() > +is made should already have be ioremap'd with write-combining page attributes > +or PAT entries, this can be done by using ioremap_wc() / or respective helpers. > +Devices which combine areas of IO memory desired to remain uncachable with I would spell it uncacheable. In kernel Documentation/, grep uncacheable finds 14 hits vs. 6 hits for uncachable. No big deal. > +areas where write-combining is desirable and are restricted by the size > +requirements of MTRRs should consider splitting up their IO memory space > +cleanly with ioremap_uc() and ioremap_wc() followed by an arch_phys_wc_add() > +encompassing both regions. Such use is nevertheless heavily discouraged as > +the effective memory type is considered implementation defined. This strategy > +should only be used as last resort on devices with size-contrained regions size-constrained > +where otherwise MTRR write-combining would not be effective. > + > +Note that you cannot use set_memory_wc() to override / whitelist IO remapped > +memory space mapped with ioremap*() calls, set_memory_wc() can only be used > +on RAM. > + > +---------------------------------------------------------------------- > +MTRR Non-PAT PAT Linux ioremap value Effective memory type > +---------------------------------------------------------------------- > + Non-PAT | PAT > + PAT > + |PCD > + ||PWT > + ||| > +WC 000 WB _PAGE_CACHE_MODE_WB WC | WC > +WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC > +WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | WC > +WC 011 UC _PAGE_CACHE_MODE_UC UC | UC > +---------------------------------------------------------------------- > + > +(*) denotes implementation defined and is discouraged > > Notes: > > diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c > index ea5f363..12abdbe 100644 > --- a/arch/x86/kernel/cpu/mtrr/main.c > +++ b/arch/x86/kernel/cpu/mtrr/main.c > @@ -538,6 +538,9 @@ EXPORT_SYMBOL(mtrr_del); > * attempts to add a WC MTRR covering size bytes starting at base and > * logs an error if this fails. > * > + * The caller should expect to need to provide a power of two size on an * The called should provide a power of two size on an equivalent * power of two boundary. > + * equivalent power of two boundary. > + * > * Drivers must store the return value to pass to mtrr_del_wc_if_needed, > * but drivers should not try to interpret that return value. > */ > -- ~Randy From mboxrd@z Thu Jan 1 00:00:00 1970 From: Randy Dunlap Date: Thu, 30 Apr 2015 22:01:12 +0000 Subject: Re: [PATCH v4 2/6] x86: document WC MTRR effects on PAT / non-PAT pages Message-Id: <5542A628.8050705@infradead.org> List-Id: References: <1430343851-967-1-git-send-email-mcgrof@do-not-panic.com> <1430343851-967-3-git-send-email-mcgrof@do-not-panic.com> In-Reply-To: <1430343851-967-3-git-send-email-mcgrof@do-not-panic.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Luis R. Rodriguez" , mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, bp@suse.de, plagnioj@jcrosoft.com, tomi.valkeinen@ti.com, daniel.vetter@intel.com, airlied@linux.ie Cc: dledford@redhat.com, awalls@md.metrocast.net, syrjala@sci.fi, luto@amacapital.net, mst@redhat.com, cocci@systeme.lip6.fr, linux-kernel@vger.kernel.org, "Luis R. Rodriguez" , Toshi Kani , Jonathan Corbet , Dave Hansen , Suresh Siddha , Juergen Gross , Daniel Vetter , Dave Airlie , Antonino Daplas , Mel Gorman , Vlastimil Babka , Davidlohr Bueso , linux-fbdev@vger.kernel.org On 04/29/15 14:44, Luis R. Rodriguez wrote: > From: "Luis R. Rodriguez" > > --- > Documentation/x86/mtrr.txt | 18 +++++++++++++++--- > Documentation/x86/pat.txt | 40 +++++++++++++++++++++++++++++++++++++++- > arch/x86/kernel/cpu/mtrr/main.c | 3 +++ > 3 files changed, 57 insertions(+), 4 deletions(-) > > diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt > index cf08c9f..7e183e3 100644 > --- a/Documentation/x86/pat.txt > +++ b/Documentation/x86/pat.txt > @@ -102,7 +104,43 @@ wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc() > as step 0 above and also track the usage of those pages and use set_memory_wb() > before the page is freed to free pool. > > - > +MTRR effects on PAT / non-PAT systems > +------------------------------------- > + > +The following table provides the effects of using write-combining MTRRs when > +using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally > +mtrr_add() usage will be phased in favor of arch_phys_wc_add() which will > +be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add() > +is made should already have be ioremap'd with write-combining page attributes > +or PAT entries, this can be done by using ioremap_wc() / or respective helpers. > +Devices which combine areas of IO memory desired to remain uncachable with I would spell it uncacheable. In kernel Documentation/, grep uncacheable finds 14 hits vs. 6 hits for uncachable. No big deal. > +areas where write-combining is desirable and are restricted by the size > +requirements of MTRRs should consider splitting up their IO memory space > +cleanly with ioremap_uc() and ioremap_wc() followed by an arch_phys_wc_add() > +encompassing both regions. Such use is nevertheless heavily discouraged as > +the effective memory type is considered implementation defined. This strategy > +should only be used as last resort on devices with size-contrained regions size-constrained > +where otherwise MTRR write-combining would not be effective. > + > +Note that you cannot use set_memory_wc() to override / whitelist IO remapped > +memory space mapped with ioremap*() calls, set_memory_wc() can only be used > +on RAM. > + > +---------------------------------------------------------------------- > +MTRR Non-PAT PAT Linux ioremap value Effective memory type > +---------------------------------------------------------------------- > + Non-PAT | PAT > + PAT > + |PCD > + ||PWT > + ||| > +WC 000 WB _PAGE_CACHE_MODE_WB WC | WC > +WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC > +WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | WC > +WC 011 UC _PAGE_CACHE_MODE_UC UC | UC > +---------------------------------------------------------------------- > + > +(*) denotes implementation defined and is discouraged > > Notes: > > diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c > index ea5f363..12abdbe 100644 > --- a/arch/x86/kernel/cpu/mtrr/main.c > +++ b/arch/x86/kernel/cpu/mtrr/main.c > @@ -538,6 +538,9 @@ EXPORT_SYMBOL(mtrr_del); > * attempts to add a WC MTRR covering size bytes starting at base and > * logs an error if this fails. > * > + * The caller should expect to need to provide a power of two size on an * The called should provide a power of two size on an equivalent * power of two boundary. > + * equivalent power of two boundary. > + * > * Drivers must store the return value to pass to mtrr_del_wc_if_needed, > * but drivers should not try to interpret that return value. > */ > -- ~Randy