[PATCH v2 02/22] asm-generic/io.h: add ioremap_nopost remap interface

[Lorenzo Pieralisi]

The PCI specifications (Rev 3.0, 3.2.5 "Transaction Ordering and
Posting") mandate non-posted configuration transactions. As further
highlighted in the PCIe specifications (4.0 - Rev0.3, "Ordering
Considerations for the Enhanced Configuration Access Mechanism"),
through ECAM and ECAM-derivative configuration mechanism, the memory
mapped transactions from the host CPU into Configuration Requests on the
PCI express fabric may create ordering problems for software because
writes to memory address are typically posted transactions (unless the
architecture can enforce through virtual address mapping non-posted
write transactions behaviour) but writes to Configuration Space are not
posted on the PCI express fabric.

Current DT and ACPI host bridge controllers map PCI configuration space
(ECAM and ECAM-derivative) into the virtual address space through
ioremap() calls, that are non-cacheable device accesses on most
architectures, but may provide "bufferable" or "posted" write semantics
in architecture like eg ARM/ARM64 that allow ioremap'ed regions writes
to be buffered in the bus connecting the host CPU to the PCI fabric;
this behaviour, as underlined in the PCIe specifications, may trigger
transactions ordering rules and must be prevented.

Introduce a new generic and explicit API to create a memory
mapping for ECAM and ECAM-derivative config space area that
defaults to ioremap_nocache() (which should provide a sane default
behaviour) but still allowing architectures on which ioremap_nocache()
results in posted write transactions to override the function
call with an arch specific implementation that complies with
the PCI specifications for configuration transactions.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>
---
 arch/alpha/include/asm/io.h | 1 +
 arch/avr32/include/asm/io.h | 1 +
 arch/frv/include/asm/io.h   | 1 +
 arch/ia64/include/asm/io.h  | 1 +
 arch/x86/include/asm/io.h   | 1 +
 include/asm-generic/io.h    | 4 ++++
 6 files changed, 9 insertions(+)

diff --git a/arch/alpha/include/asm/io.h b/arch/alpha/include/asm/io.h
index ff40491..27379ea 100644
--- a/arch/alpha/include/asm/io.h
+++ b/arch/alpha/include/asm/io.h
@@ -300,6 +300,7 @@ static inline void __iomem * ioremap_nocache(unsigned long offset,
 }
 
 #define ioremap_uc ioremap_nocache
+#define ioremap_nopost ioremap_nocache
 
 static inline void iounmap(volatile void __iomem *addr)
 {
diff --git a/arch/avr32/include/asm/io.h b/arch/avr32/include/asm/io.h
index f855646..3f1ced8 100644
--- a/arch/avr32/include/asm/io.h
+++ b/arch/avr32/include/asm/io.h
@@ -298,6 +298,7 @@ extern void __iounmap(void __iomem *addr);
 #define ioremap_wc ioremap_nocache
 #define ioremap_wt ioremap_nocache
 #define ioremap_uc ioremap_nocache
+#define ioremap_nopost ioremap_nocache
 
 #define cached(addr) P1SEGADDR(addr)
 #define uncached(addr) P2SEGADDR(addr)
diff --git a/arch/frv/include/asm/io.h b/arch/frv/include/asm/io.h
index 8062fc7..302fb8c 100644
--- a/arch/frv/include/asm/io.h
+++ b/arch/frv/include/asm/io.h
@@ -290,6 +290,7 @@ static inline void __iomem *ioremap_fullcache(unsigned long physaddr, unsigned l
 
 #define ioremap_wc ioremap_nocache
 #define ioremap_uc ioremap_nocache
+#define ioremap_nopost ioremap_nocache
 
 extern void iounmap(void volatile __iomem *addr);
 
diff --git a/arch/ia64/include/asm/io.h b/arch/ia64/include/asm/io.h
index 5de673a..70a4985 100644
--- a/arch/ia64/include/asm/io.h
+++ b/arch/ia64/include/asm/io.h
@@ -434,6 +434,7 @@ static inline void __iomem * ioremap_cache (unsigned long phys_addr, unsigned lo
 }
 #define ioremap_cache ioremap_cache
 #define ioremap_uc ioremap_nocache
+#define ioremap_nopost ioremap_nocache
 
 
 /*
diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 7afb0e2..50b292f 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -171,6 +171,7 @@ static inline unsigned int isa_virt_to_bus(volatile void *address)
 extern void __iomem *ioremap_nocache(resource_size_t offset, unsigned long size);
 extern void __iomem *ioremap_uc(resource_size_t offset, unsigned long size);
 #define ioremap_uc ioremap_uc
+#define ioremap_nopost ioremap_nocache
 
 extern void __iomem *ioremap_cache(resource_size_t offset, unsigned long size);
 extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, unsigned long prot_val);
diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index 7ef015e..0e81938 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -915,6 +915,10 @@ extern void ioport_unmap(void __iomem *p);
 #endif /* CONFIG_GENERIC_IOMAP */
 #endif /* CONFIG_HAS_IOPORT_MAP */
 
+#ifndef ioremap_nopost
+#define ioremap_nopost ioremap_nocache
+#endif
+
 #ifndef xlate_dev_kmem_ptr
 #define xlate_dev_kmem_ptr xlate_dev_kmem_ptr
 static inline void *xlate_dev_kmem_ptr(void *addr)
-- 
2.10.0