dma-mapping-broken.h: flesh-out DMA API stubs

This allows some drivers compile on arches that don't support DMA (e.g. s390).

---
Is there any reason why this header should not cover the whole DMA API?

Compile-tested only...

 include/asm-generic/dma-mapping-broken.h |  134 ++++++++++++++++++++++++++++++
 1 files changed, 134 insertions(+), 0 deletions(-)

index 29413d3..84812dd 100644
@@ -21,4 +21,116 @@ dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
 #define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
 #define dma_free_noncoherent(d, s, v, h) dma_free_coherent(d, s, v, h)
 
+static inline dma_addr_t
+dma_map_single(struct device *dev, void *ptr, size_t size,
+	       enum dma_data_direction direction)
+{
+	BUG();
+	return (dma_addr_t)0;
+}
+
+static inline void
+dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
+		 enum dma_data_direction direction)
+{
+	BUG();
+}
+
+static inline int
+dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+	   enum dma_data_direction direction)
+{
+	BUG();
+	return 0;
+}
+
+static inline void
+dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nhwentries,
+	     enum dma_data_direction direction)
+{
+	BUG();
+}
+
+static inline dma_addr_t
+dma_map_page(struct device *dev, struct page *page, unsigned long offset,
+	     size_t size, enum dma_data_direction direction)
+{
+	BUG();
+	return (dma_addr_t)0;
+}
+
+static inline void
+dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
+	       enum dma_data_direction direction)
+{
+	BUG();
+}
+
+static inline void
+dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
+			enum dma_data_direction direction)
+{
+	BUG();
+}
+
+static inline void
+dma_sync_single_range_for_cpu(struct device *dev, dma_addr_t dma_handle,
+			      unsigned long offset, size_t size,
+			      enum dma_data_direction direction)
+{
+	BUG();
+}
+
+static inline void
+dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
+		    enum dma_data_direction direction)
+{
+	BUG();
+}
+
+#define dma_sync_single_for_device dma_sync_single_for_cpu
+#define dma_sync_single_range_for_device dma_sync_single_range_for_cpu
+#define dma_sync_sg_for_device dma_sync_sg_for_cpu
+
+static inline int
+dma_mapping_error(dma_addr_t dma_addr)
+{
+	BUG();
+	return 1;
+}
+
+static inline int
+dma_supported(struct device *dev, u64 mask)
+{
+	return 0;
+}
+
+static inline int
+dma_set_mask(struct device *dev, u64 mask)
+{
+	BUG();
+	return -EIO;
+}
+
+static inline int
+dma_get_cache_alignment(void)
+{
+	BUG();
+	return 0;
+}
+
+int
+dma_is_consistent(struct device *dev, dma_addr_t dma_handle)
+{
+	BUG();
+	return 0;
+}
+
+static inline void
+dma_cache_sync(struct device *dev, void *vaddr, size_t size,
+	       enum dma_data_direction direction)
+{
+	BUG();
+}
+
 #endif /* _ASM_GENERIC_DMA_MAPPING_H */

1.4.4.2

Which drivers are we talking about? Last time I checked an allmodconfig just compiled.
I'd rather like to the opposite: rip out everything that depends on DMA (via e.g. CONFIG_HAS_DMA), so we don't have to compile in all the unused code. If that is is possible...

Heiko Carstens
Linux on System z Development

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen
Geschaeftsfuehrung : Herbert Kircher
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

How about this for telling that an architecture doesn't support DMA? At least we could get rid of dma-mapping-broken.h and don't need to compile some afterwards dead code.

---
 arch/s390/Kconfig              |    3 +++
 drivers/base/Makefile          |    4 ++--
 include/asm-s390/dma-mapping.h |    2 --
 lib/Kconfig                    |    5 +++++
 4 files changed, 10 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/s390/Kconfig
===================================================================
@@ -44,6 +44,9 @@ config GENERIC_TIME
 config NO_IOMEM
 	def_bool y
 
+config NO_DMA
+	def_bool y
+
 mainmenu "Linux Kernel Configuration"
 
 config S390

Index: linux-2.6/drivers/base/Makefile
===================================================================
@@ -2,10 +2,10 @@
 
 obj-y			:= core.o sys.o bus.o dd.o \
 			   driver.o class.o platform.o \
-			   cpu.o firmware.o init.o map.o dmapool.o \
-			   dma-mapping.o devres.o \
+			   cpu.o firmware.o init.o map.o devres.o \
 			   attribute_container.o transport_class.o
 obj-y			+= power/
+obj-$(CONFIG_DMA)	+= dma-mapping.o dmapool.o
 obj-$(CONFIG_ISA)	+= isa.o
 obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
 obj-$(CONFIG_NUMA)	+= node.o

Index: linux-2.6/include/asm-s390/dma-mapping.h
===================================================================
@@ -9,6 +9,4 @@
 #ifndef _ASM_DMA_MAPPING_H
 #define _ASM_DMA_MAPPING_H
 
-#include <asm-generic/dma-mapping-broken.h>
-
 #endif /* _ASM_DMA_MAPPING_H */

Index: linux-2.6/lib/Kconfig
===================================================================
@@ -111,4 +111,9 @@ config HAS_IOPORT
 	depends on HAS_IOMEM && !NO_IOPORT
 	default y
 
+config HAS_DMA
+	boolean
+	depends on !NO_DMA
+	default y
+
 endmenu

Heiko Carstens
Linux on System z Development

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen
Geschaeftsfuehrung : Herbert Kircher
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

This like a lot better of an idea than stubbing out things which should never be built in the first place...

Cheers,
Kyle

My only thought was that the intent must have been to allow compilation of a driver that checks for DMA at runtime (via dma_supported). But, I guess dma_supported is intended as a platform-level check?

If the DMA availability is at the arch level then such a driver could use (albeit ugly) compile flags to cover that situation...?

Well, either way is fine with me.

John

John W. Linville
[email protected]

From: Heiko Carstens <[email protected]>

Architectures that don't support DMA can say so by adding a config NO_DMA to their Kconfig file. This will prevent compilation of some dma specific driver code. Also dma-mapping-broken.h isn't needed anymore on at least s390.
This avoids compilation and linking of otherwise dead/broken code.

---

Other architectures that include dma-mapping-broken.h are arm26, h8300, m68k, m68knommu and v850. If these could be converted as well we could get rid of the header file.

 arch/s390/Kconfig              |    3 +++
 drivers/base/Makefile          |    4 ++--
 include/asm-s390/dma-mapping.h |    2 --
 lib/Kconfig                    |    5 +++++
 4 files changed, 10 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/s390/Kconfig
===================================================================
@@ -44,6 +44,9 @@ config GENERIC_TIME
 config NO_IOMEM
 	def_bool y
 
+config NO_DMA
+	def_bool y
+
 mainmenu "Linux Kernel Configuration"
 
 config S390

Index: linux-2.6/drivers/base/Makefile
===================================================================
@@ -2,10 +2,10 @@
 
 obj-y			:= core.o sys.o bus.o dd.o \
 			   driver.o class.o platform.o \
-			   cpu.o firmware.o init.o map.o dmapool.o \
-			   dma-mapping.o devres.o \
+			   cpu.o firmware.o init.o map.o devres.o \
 			   attribute_container.o transport_class.o
 obj-y			+= power/
+obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o dmapool.o
 obj-$(CONFIG_ISA)	+= isa.o
 obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
 obj-$(CONFIG_NUMA)	+= node.o

Index: linux-2.6/include/asm-s390/dma-mapping.h
===================================================================
@@ -9,6 +9,4 @@
 #ifndef _ASM_DMA_MAPPING_H
 #define _ASM_DMA_MAPPING_H
 
-#include <asm-generic/dma-mapping-broken.h>
-
 #endif /* _ASM_DMA_MAPPING_H */

Index: linux-2.6/lib/Kconfig
===================================================================
@@ -111,4 +111,9 @@ config HAS_IOPORT
 	depends on HAS_IOMEM && !NO_IOPORT
 	default y
 
+config HAS_DMA
+	boolean
+	depends on !NO_DMA
+	default y
+
 endmenu

Heiko Carstens
Linux on System z Development

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen
Geschaeftsfuehrung : Herbert Kircher
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

[ apologies for reviving an old conversation ]

I went back and read the thread leading up to this patch and I am of the opinion that John's approach (adding more stubs to dma-mapping-broken.h:
http://marc.info/?l=linux-kernel&m=117219377712232&w=2) is needed in _addition_ to this Kconfig option. In my particular case I have an API with a DMA and a non-DMA path written in such a way that the DMA path can be compiled away. Without dma-mapping-broken.h support the API is unnecessarily forced to violate point 2 of Documentation/SubmittingPatches (#ifdefs are ugly).

In other words let CONFIG_HAS_DMA prevent pure DMA code from being built, but do not preclude "clever" implementations from calling broken code.

If there are no objections I plan to resubmit John's changes with the addition below, which allows CONFIG_HAS_DMA=n architectures to delete their respective dma-mapping.h file.

index 9a663c6..2dc21cb 100644
@@ -31,7 +31,11 @@ static inline int valid_dma_direction(int dma_direction)
               (dma_direction == DMA_FROM_DEVICE));

}

+#ifdef CONFIG_HAS_DMA
#include <asm/dma-mapping.h>
+#else
+#include <asm-generic/dma-mapping-broken.h>
+#endif

/* Backwards compat, remove in 2.7.x */
#define dma_sync_single dma_sync_single_for_cpu

IMO, well-placed #ifdefs are preferrable to dragging non-working code around. Like:

- put the DMA path in a file only build for MY_STUFF_USE_DMA
- let MY_STUFF select MY_STUFF_USE_DMA if HAS_DMA
- have a header file that points to the implementation for MY_STUFF_USE_DMA and uses well defined stubs for !MY_STUFF_USE_DMA, like returning ICannotDoThat for check_if_can_do() (kind of like what include/linux/sysfs.h does, for example)

This contains the #ifdefs in a header, doesn't compile stuff that won't work anyway on !HAS_DMA, and adds the ability to disable MY_STUFF_USE_DMA even if HAS_DMA at a later time if someone wants it.

If it calls broken code, it may not be so "clever" after all :)

What I don't like about this is

- compiles stuff that is not needed on !HAS_DMA
- worse, compiles stuff that will not work on !HAS_DMA
- does not encourage to split code properly into a DMA and a non-DMA part

[ please let me know if you want to be dropped from the cc ]

what

won't

Yes, at run time, but not necessarily at compile time.

I came to the same conclusions as I started to implement the bug-stubs. The patch (to follow) attempts to satisfy all the concerns you outline as well as my observation that async_tx requires no factoring for the !HAS_DMA case.

With the patch non-dma-architectures that try to build code with true dependencies on the DMA api will fail to link i.e.:

CONFIG_DMA_ENGINE=y CONFIG_HAS_DMA=n ASYNC_MEMCPY=y

  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1

async_tx/built-in.o: In function `async_memcpy':
xor.c:(.text+0x770): undefined reference to dma_map_page' xor.c:(.text+0x798): undefined reference to dma_map_page' xor.c:(.text+0x968): undefined reference to `dma_map_page'

Now changing CONFIG_DMA_ENGINE to depend on HAS_DMA (which is more correct than saying !S390). Results in:
CONFIG_DMA_ENGINE=n CONFIG_HAS_DMA=n ASYNC_MEMCPY=y

  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
  KSYM    .tmp_kallsyms1.S
  AS      .tmp_kallsyms1.o
  LD      .tmp_vmlinux2
  KSYM    .tmp_kallsyms2.S
  AS      .tmp_kallsyms2.o
  LD      vmlinux

This also allows include/asm-s390/dma-mapping.h to be dropped.

Dan

Continuing the work started in 411f0f3edc141a582190d3605cadd1d993abb6df ...

This enables code with a dma path, that compiles away, to build without requiring additional code factoring. It also prevents code that calls dma_alloc_coherent and dma_free_coherent from linking whereas previously the code would hit a BUG() at run time. Finally, it allows archs that set !HAS_DMA to delete their asm/dma-mapping.h file.

---

 arch/arm26/Kconfig                       |    3 +
 arch/h8300/Kconfig                       |    3 +
 arch/m32r/Kconfig                        |    3 +
 drivers/dma/Kconfig                      |    2 -
 include/asm-arm26/dma-mapping.h          |    2 -
 include/asm-generic/dma-mapping-broken.h |   82 ++++++++++++++++++++++++++----
 include/asm-h8300/dma-mapping.h          |    1 
 include/asm-m32r/dma-mapping.h           |    6 --
 include/asm-s390/dma-mapping.h           |   12 ----
 include/linux/dma-mapping.h              |    4 +
 10 files changed, 84 insertions(+), 34 deletions(-)

index 20688bc..9044f33 100644
@@ -17,6 +17,9 @@ config MMU
 	bool
 	default y
 
+config NO_DMA
+	def_bool y
+
 config ARCH_ACORN
         bool
         default y

index 618dbad..e35f74e 100644
@@ -68,6 +68,9 @@ config TIME_LOW_RES
 config NO_IOPORT
 	def_bool y
 
+config NO_DMA
+	def_bool y
+
 config ISA
 	bool
 	default y

index c3bb8a7..8ccf3e4 100644
@@ -31,6 +31,9 @@ config GENERIC_IRQ_PROBE
 config NO_IOPORT
 	def_bool y
 
+config NO_DMA
+	def_bool y
+
 source "init/Kconfig"
 
 

index 72be6c6..59305bc 100644
@@ -3,7 +3,7 @@
 #
 
 menu "DMA Engine support"
-	depends on !S390
+	depends on HAS_DMA
 
 config DMA_ENGINE
 	bool "Support for DMA engines"

deleted file mode 100644
index a95eae0..0000000
@@ -1,2 +0,0 @@
-#include <asm-generic/dma-mapping-broken.h>
-

deleted file mode 100644
index d00e400..0000000
@@ -1 +0,0 @@
-#include <asm-generic/dma-mapping-broken.h>

deleted file mode 100644
index f9b58eb..0000000
@@ -1,6 +0,0 @@
-#ifndef _ASM_M32R_DMA_MAPPING_H
-#define _ASM_M32R_DMA_MAPPING_H
-
-#include <asm-generic/dma-mapping-broken.h>
-
-#endif /* _ASM_M32R_DMA_MAPPING_H */

deleted file mode 100644
index 3f8c12f..0000000
@@ -1,12 +0,0 @@
-/*
- *  include/asm-s390/dma-mapping.h
- *
- *  S390 version
- *
- *  This file exists so that #include <dma-mapping.h> doesn't break anything.
- */
-
-#ifndef _ASM_DMA_MAPPING_H
-#define _ASM_DMA_MAPPING_H
-
-#endif /* _ASM_DMA_MAPPING_H */

index 9a663c6..2dc21cb 100644
@@ -31,7 +31,11 @@ static inline int valid_dma_direction(int dma_direction)
 		(dma_direction == DMA_FROM_DEVICE));
 }
 
+#ifdef CONFIG_HAS_DMA
 #include <asm/dma-mapping.h>
+#else
+#include <asm-generic/dma-mapping-broken.h>
+#endif
 
 /* Backwards compat, remove in 2.7.x */
 #define dma_sync_single		dma_sync_single_for_cpu

Makes sense.

Cool. Thanks for looking into that.