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authorLuis R. Rodriguez <mcgrof@suse.com>2015-05-11 10:15:53 +0200
committerIngo Molnar <mingo@kernel.org>2015-05-11 10:38:45 +0200
commite4b6be33c28923d8cde53023e0888b1c5d1a9027 (patch)
tree5faf5973dcffda3df916b173e499a8695ba5a5ad /include/asm-generic
parentcd2f6a5a4704a359635eb34919317052e6a96ba7 (diff)
x86/mm: Add ioremap_uc() helper to map memory uncacheable (not UC-)
ioremap_nocache() currently uses UC- by default. Our goal is to eventually make UC the default. Linux maps UC- to PCD=1, PWT=0 page attributes on non-PAT systems. Linux maps UC to PCD=1, PWT=1 page attributes on non-PAT systems. On non-PAT and PAT systems a WC MTRR has different effects on pages with either of these attributes. In order to help with a smooth transition its best to enable use of UC (PCD,1, PWT=1) on a region as that ensures a WC MTRR will have no effect on a region, this however requires us to have an way to declare a region as UC and we currently do not have a way to do this. WC MTRR on non-PAT system with PCD=1, PWT=0 (UC-) yields WC. WC MTRR on non-PAT system with PCD=1, PWT=1 (UC) yields UC. WC MTRR on PAT system with PCD=1, PWT=0 (UC-) yields WC. WC MTRR on PAT system with PCD=1, PWT=1 (UC) yields UC. A flip of the default ioremap_nocache() behaviour from UC- to UC can therefore regress a memory region from effective memory type WC to UC if MTRRs are used. Use of MTRRs should be phased out and in the best case only arch_phys_wc_add() use will remain, even if this happens arch_phys_wc_add() will have an effect on non-PAT systems and changes to default ioremap_nocache() behaviour could regress drivers. Now, ideally we'd use ioremap_nocache() on the regions in which we'd need uncachable memory types and avoid any MTRRs on those regions. There are however some restrictions on MTRRs use, such as the requirement of having the base and size of variable sized MTRRs to be powers of two, which could mean having to use a WC MTRR over a large area which includes a region in which write-combining effects are undesirable. Add ioremap_uc() to help with the both phasing out of MTRR use and also provide a way to blacklist small WC undesirable regions in devices with mixed regions which are size-implicated to use large WC MTRRs. Use of ioremap_uc() helps phase out MTRR use by avoiding regressions with an eventual flip of default behaviour or ioremap_nocache() from UC- to UC. Drivers working with WC MTRRs can use the below table to review and consider the use of ioremap*() and similar helpers to ensure appropriate behaviour long term even if default ioremap_nocache() behaviour changes from UC- to UC. Although ioremap_uc() is being added we leave set_memory_uc() to use UC- as only initial memory type setup is required to be able to accommodate existing device drivers and phase out MTRR use. It should also be clarified that set_memory_uc() cannot be used with IO memory, even though its use will not return any errors, it really has no effect. ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Antonino Daplas <adaplas@gmail.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dave Airlie <airlied@redhat.com> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Travis <travis@sgi.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Suresh Siddha <sbsiddha@gmail.com> Cc: Thierry Reding <treding@nvidia.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Cc: Toshi Kani <toshi.kani@hp.com> Cc: Ville Syrjälä <syrjala@sci.fi> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-fbdev@vger.kernel.org Link: http://lkml.kernel.org/r/1430343851-967-2-git-send-email-mcgrof@do-not-panic.com Link: http://lkml.kernel.org/r/1431332153-18566-9-git-send-email-bp@alien8.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/asm-generic')
-rw-r--r--include/asm-generic/io.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index 9db042304df3..90ccba7f9f9a 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -769,6 +769,14 @@ static inline void __iomem *ioremap_nocache(phys_addr_t offset, size_t size)
}
#endif
+#ifndef ioremap_uc
+#define ioremap_uc ioremap_uc
+static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
+{
+ return ioremap_nocache(offset, size);
+}
+#endif
+
#ifndef ioremap_wc
#define ioremap_wc ioremap_wc
static inline void __iomem *ioremap_wc(phys_addr_t offset, size_t size)