[PATCH v5 5/7] ARM: NOMMU: Introduce dma operations for noMMU

[Vladimir Murzin]

R/M classes of cpus can have memory covered by MPU which in turn might
configure RAM as Normal i.e. bufferable and cacheable. It breaks
dma_alloc_coherent() and friends, since data can stuck in caches now
or be buffered.

This patch factors out DMA support for NOMMU configuration into
separate entity which provides dedicated dma_ops. We have to handle
there several cases:
- configurations with MMU/MPU setup
- configurations without MMU/MPU setup
- special case for M-class, since caches and MPU there are optional

In general we rely on default DMA area for coherent allocations or/and
per-device memory reserves suitable for coherent DMA, so if such
regions are set coherent allocations go from there.

In case MMU/MPU was not setup we fallback to normal page allocator for
DMA memory allocation.

In case we run M-class cpus, for configuration without cache support
(like Cortex-M3/M4) dma operations are forced to be coherent and wired
with dma-noop (such decision is made based on cacheid global
variable); however, if caches are detected there and no DMA coherent
region is given (either default or per-device), dma is disallowed even
MPU is not set - it is because M-class implement system memory map
which defines part of address space as Normal memory.

Reported-by: Alexandre Torgue 
Reported-by: Andras Szemzo 
Tested-by: Benjamin Gaignard 
Tested-by: Andras Szemzo 
Tested-by: Alexandre TORGUE 
Reviewed-by: Robin Murphy 
Signed-off-by: Vladimir Murzin 
Acked-by: Arnd Bergmann 
---
 arch/arm/Kconfig   |   1 +
 arch/arm/include/asm/dma-mapping.h |   2 +-
 arch/arm/mm/Makefile   |   5 +-
 arch/arm/mm/dma-mapping-nommu.c| 253 +
 4 files changed, 257 insertions(+), 4 deletions(-)
 create mode 100644 arch/arm/mm/dma-mapping-nommu.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ed801f0..98e15d0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -22,6 +22,7 @@ config ARM
select CLONE_BACKWARDS
select CPU_PM if (SUSPEND || CPU_IDLE)
select DCACHE_WORD_ACCESS if HAVE_EFFICIENT_UNALIGNED_ACCESS
+   select DMA_NOOP_OPS if !MMU
select EDAC_SUPPORT
select EDAC_ATOMIC_SCRUB
select GENERIC_ALLOCATOR
diff --git a/arch/arm/include/asm/dma-mapping.h 
b/arch/arm/include/asm/dma-mapping.h
index 680d3f3..0eec080 100644
--- a/arch/arm/include/asm/dma-mapping.h
+++ b/arch/arm/include/asm/dma-mapping.h
@@ -18,7 +18,7 @@ extern const struct dma_map_ops arm_coherent_dma_ops;
 
 static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 {
-   return _dma_ops;
+   return IS_ENABLED(CONFIG_MMU) ? _dma_ops : _noop_ops;
 }
 
 #define HAVE_ARCH_DMA_SUPPORTED 1
diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
index 54857bc..ea80df7 100644
--- a/arch/arm/mm/Makefile
+++ b/arch/arm/mm/Makefile
@@ -2,9 +2,8 @@
 # Makefile for the linux arm-specific parts of the memory manager.
 #
 
-obj-y  := dma-mapping.o extable.o fault.o init.o \
-  iomap.o
-
+obj-y  := extable.o fault.o init.o iomap.o
+obj-y  += dma-mapping$(MMUEXT).o
 obj-$(CONFIG_MMU)  += fault-armv.o flush.o idmap.o ioremap.o \
   mmap.o pgd.o mmu.o pageattr.o
 
diff --git a/arch/arm/mm/dma-mapping-nommu.c b/arch/arm/mm/dma-mapping-nommu.c
new file mode 100644
index 000..3ba3003
--- /dev/null
+++ b/arch/arm/mm/dma-mapping-nommu.c
@@ -0,0 +1,253 @@
+/*
+ *  Based on linux/arch/arm/mm/dma-mapping.c
+ *
+ *  Copyright (C) 2000-2004 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include 
+#include 
+#include 
+#include 
+
+#include 
+#include 
+#include 
+#include 
+
+#include "dma.h"
+
+/*
+ *  dma_noop_ops is used if
+ *   - MMU/MPU is off
+ *   - cpu is v7m w/o cache support
+ *   - device is coherent
+ *  otherwise arm_nommu_dma_ops is used.
+ *
+ *  arm_nommu_dma_ops rely on consistent DMA memory (please, refer to
+ *  [1] on how to declare such memory).
+ *
+ *  [1] Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+ */
+
+static void *arm_nommu_dma_alloc(struct device *dev, size_t size,
+dma_addr_t *dma_handle, gfp_t gfp,
+unsigned long attrs)
+
+{
+   const struct dma_map_ops *ops = _noop_ops;
+
+   /*
+* We are here because:
+* - no consistent DMA region has been defined, so we can't
+*   continue.
+* - there is no space left in consistent DMA region, so we
+*   only can fallback to generic allocator if we 

[PATCH v5 5/7] ARM: NOMMU: Introduce dma operations for noMMU

[Vladimir Murzin]

R/M classes of cpus can have memory covered by MPU which in turn might
configure RAM as Normal i.e. bufferable and cacheable. It breaks
dma_alloc_coherent() and friends, since data can stuck in caches now
or be buffered.

This patch factors out DMA support for NOMMU configuration into
separate entity which provides dedicated dma_ops. We have to handle
there several cases:
- configurations with MMU/MPU setup
- configurations without MMU/MPU setup
- special case for M-class, since caches and MPU there are optional

In general we rely on default DMA area for coherent allocations or/and
per-device memory reserves suitable for coherent DMA, so if such
regions are set coherent allocations go from there.

In case MMU/MPU was not setup we fallback to normal page allocator for
DMA memory allocation.

In case we run M-class cpus, for configuration without cache support
(like Cortex-M3/M4) dma operations are forced to be coherent and wired
with dma-noop (such decision is made based on cacheid global
variable); however, if caches are detected there and no DMA coherent
region is given (either default or per-device), dma is disallowed even
MPU is not set - it is because M-class implement system memory map
which defines part of address space as Normal memory.

Reported-by: Alexandre Torgue 
Reported-by: Andras Szemzo 
Tested-by: Benjamin Gaignard 
Tested-by: Andras Szemzo 
Tested-by: Alexandre TORGUE 
Reviewed-by: Robin Murphy 
Signed-off-by: Vladimir Murzin 
Acked-by: Arnd Bergmann 
---
 arch/arm/Kconfig   |   1 +
 arch/arm/include/asm/dma-mapping.h |   2 +-
 arch/arm/mm/Makefile   |   5 +-
 arch/arm/mm/dma-mapping-nommu.c| 253 +
 4 files changed, 257 insertions(+), 4 deletions(-)
 create mode 100644 arch/arm/mm/dma-mapping-nommu.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ed801f0..98e15d0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -22,6 +22,7 @@ config ARM
select CLONE_BACKWARDS
select CPU_PM if (SUSPEND || CPU_IDLE)
select DCACHE_WORD_ACCESS if HAVE_EFFICIENT_UNALIGNED_ACCESS
+   select DMA_NOOP_OPS if !MMU
select EDAC_SUPPORT
select EDAC_ATOMIC_SCRUB
select GENERIC_ALLOCATOR
diff --git a/arch/arm/include/asm/dma-mapping.h 
b/arch/arm/include/asm/dma-mapping.h
index 680d3f3..0eec080 100644
--- a/arch/arm/include/asm/dma-mapping.h
+++ b/arch/arm/include/asm/dma-mapping.h
@@ -18,7 +18,7 @@ extern const struct dma_map_ops arm_coherent_dma_ops;
 
 static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 {
-   return _dma_ops;
+   return IS_ENABLED(CONFIG_MMU) ? _dma_ops : _noop_ops;
 }
 
 #define HAVE_ARCH_DMA_SUPPORTED 1
diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
index 54857bc..ea80df7 100644
--- a/arch/arm/mm/Makefile
+++ b/arch/arm/mm/Makefile
@@ -2,9 +2,8 @@
 # Makefile for the linux arm-specific parts of the memory manager.
 #
 
-obj-y  := dma-mapping.o extable.o fault.o init.o \
-  iomap.o
-
+obj-y  := extable.o fault.o init.o iomap.o
+obj-y  += dma-mapping$(MMUEXT).o
 obj-$(CONFIG_MMU)  += fault-armv.o flush.o idmap.o ioremap.o \
   mmap.o pgd.o mmu.o pageattr.o
 
diff --git a/arch/arm/mm/dma-mapping-nommu.c b/arch/arm/mm/dma-mapping-nommu.c
new file mode 100644
index 000..3ba3003
--- /dev/null
+++ b/arch/arm/mm/dma-mapping-nommu.c
@@ -0,0 +1,253 @@
+/*
+ *  Based on linux/arch/arm/mm/dma-mapping.c
+ *
+ *  Copyright (C) 2000-2004 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include 
+#include 
+#include 
+#include 
+
+#include 
+#include 
+#include 
+#include 
+
+#include "dma.h"
+
+/*
+ *  dma_noop_ops is used if
+ *   - MMU/MPU is off
+ *   - cpu is v7m w/o cache support
+ *   - device is coherent
+ *  otherwise arm_nommu_dma_ops is used.
+ *
+ *  arm_nommu_dma_ops rely on consistent DMA memory (please, refer to
+ *  [1] on how to declare such memory).
+ *
+ *  [1] Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+ */
+
+static void *arm_nommu_dma_alloc(struct device *dev, size_t size,
+dma_addr_t *dma_handle, gfp_t gfp,
+unsigned long attrs)
+
+{
+   const struct dma_map_ops *ops = _noop_ops;
+
+   /*
+* We are here because:
+* - no consistent DMA region has been defined, so we can't
+*   continue.
+* - there is no space left in consistent DMA region, so we
+*   only can fallback to generic allocator if we are
+*   advertised that consistency is not required.
+*/
+
+   if (attrs & DMA_ATTR_NON_CONSISTENT)
+   return ops->alloc(dev, size,