Re: [PATCH -mm] dma-mapping.h: add the dma_unmap state API

From: FUJITA Tomonori
Date: Sat Feb 13 2010 - 01:15:29 EST

On Fri, 12 Feb 2010 20:44:05 -0800
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Sat, 13 Feb 2010 11:49:09 +0900 FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote:
>
> > On Fri, 12 Feb 2010 11:51:57 -0800
> > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > > > -#ifdef CONFIG_NEED_DMA_MAP_STATE
> > > > -#define DECLARE_PCI_UNMAP_ADDR(ADDR_NAME) dma_addr_t ADDR_NAME;
> > > > -#define DECLARE_PCI_UNMAP_LEN(LEN_NAME) __u32 LEN_NAME;
> > >
> > > But we already screwed up the semicolon thing. If you grep the tree you'll
> > > see that about half of the users of this macro added their own semicolon:
> >
> > Yeah, I know. PCI-DMA-mapping.txt says:
> >
> > NOTE: DO NOT put a semicolon at the end of the DECLARE_*() macro.
> >
> >
> > But there are some other DECLARE_ macros that don't have the
> > semicolons so users could be easily confused.
>
> yup. Users already got confused.
>
> > #define DEFINE_DMA_MAP_ADDR(ADDR_NAME) dma_addr_t ADDR_NAME
> >
> > looks better?
>
> yes. People expect to have to put the semicolon in there, so they do.

Ok, how about this instead of the previous patch?

=
From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Subject: [PATCH -mm v2] dma-mapping.h: add the dma_unmap state API

Adds the following macros:

DEFINE_DMA_UNMAP_ADDR(ADDR_NAME)
DEFINE_DMA_UNMAP_LEN(LEN_NAME)
dma_unmap_addr(PTR, ADDR_NAME)
dma_unmap_addr_set(PTR, ADDR_NAME, VAL)
dma_unmap_len(PTR, LEN_NAME)
dma_unmap_len_set(PTR, LEN_NAME, VAL)

The API corresponds to the pci_unmap state API. We'll move to this new
generic API from the PCI specific API in the long term. As
include/asm-generic/pci-dma-compat.h does, the pci_unmap API simply
calls the new generic API for some time.

Note that DEFINE_DMA_UNMAP_ADDR and DEFINE_DMA_UNMAP_LEN are slightly
different from DECLARE_PCI_UNMAP_ADDR and
DECLARE_PCI_UNMAP_LEN. Unlike DECLARE_PCI_UNMAP_ADDR and
DECLARE_PCI_UNMAP_LEN, DEFINE_DMA_UNMAP_ADDR and DEFINE_DMA_UNMAP_LEN
need a semicolon at the end of the macros. It looks more
straightforward.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
---
Documentation/DMA-API.txt | 58 +++++++++++++++++++++++++++++++++++++++++++
include/linux/dma-mapping.h | 16 ++++++++++++
include/linux/pci-dma.h | 21 ++++-----------
3 files changed, 80 insertions(+), 15 deletions(-)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index db20b37..0fc5728 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -482,6 +482,64 @@ void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
....


+Part Ie - Optimizing Unmap State Space Consumption
+--------------------------------
+
+On some platforms, dma_unmap_{single,page}() is simply a nop.
+Therefore, keeping track of the mapping address and length is a waste
+of space. Instead of filling your drivers up with ifdefs and the like
+to "work around" this (which would defeat the whole purpose of a
+portable API) the following facilities are provided.
+
+Actually, instead of describing the macros one by one, we'll
+transform some example code.
+
+1) Use DEFINE_DMA_UNMAP_{ADDR,LEN} in state saving structures.
+ Example, before:
+
+ struct ring_state {
+ struct sk_buff *skb;
+ dma_addr_t mapping;
+ __u32 len;
+ };
+
+ after:
+
+ struct ring_state {
+ struct sk_buff *skb;
+ DEFINE_DMA_UNMAP_ADDR(mapping);
+ DEFINE_DMA_UNMAP_LEN(len);
+ };
+
+2) Use dma_unmap_{addr,len}_set to set these values.
+ Example, before:
+
+ ringp->mapping = FOO;
+ ringp->len = BAR;
+
+ after:
+
+ dma_unmap_addr_set(ringp, mapping, FOO);
+ dma_unmap_len_set(ringp, len, BAR);
+
+3) Use dma_unmap_{addr,len} to access these values.
+ Example, before:
+
+ dma_unmap_single(dev, ringp->mapping, ringp->len,
+ DMA_FROM_DEVICE);
+
+ after:
+
+ dma_unmap_single(dev,
+ dma_unmap_addr(ringp, mapping),
+ dma_unmap_len(ringp, len),
+ DMA_FROM_DEVICE);
+
+It really should be self-explanatory. We treat the ADDR and LEN
+separately, because it is possible for an implementation to only
+need the address in order to perform the unmap operation.
+
+
Part II - Advanced dma_ usage
-----------------------------

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 8357721..e00c5c9 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -240,4 +240,20 @@ struct dma_attrs;

#endif /* CONFIG_HAVE_DMA_ATTRS */

+#ifdef CONFIG_NEED_DMA_MAP_STATE
+#define DEFINE_DMA_UNMAP_ADDR(ADDR_NAME) dma_addr_t ADDR_NAME
+#define DEFINE_DMA_UNMAP_LEN(LEN_NAME) __u32 LEN_NAME
+#define dma_unmap_addr(PTR, ADDR_NAME) ((PTR)->ADDR_NAME)
+#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL) (((PTR)->ADDR_NAME) = (VAL))
+#define dma_unmap_len(PTR, LEN_NAME) ((PTR)->LEN_NAME)
+#define dma_unmap_len_set(PTR, LEN_NAME, VAL) (((PTR)->LEN_NAME) = (VAL))
+#else
+#define DEFINE_DMA_MAP_ADDR(ADDR_NAME)
+#define DEFINE_DMA_UNMAP_LEN(LEN_NAME)
+#define dma_unmap_addr(PTR, ADDR_NAME) (0)
+#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL) do { } while (0)
+#define dma_unmap_len(PTR, LEN_NAME) (0)
+#define dma_unmap_len_set(PTR, LEN_NAME, VAL) do { } while (0)
+#endif
+
#endif
diff --git a/include/linux/pci-dma.h b/include/linux/pci-dma.h
index cfd63ab..549a041 100644
--- a/include/linux/pci-dma.h
+++ b/include/linux/pci-dma.h
@@ -1,20 +1,11 @@
#ifndef _LINUX_PCI_DMA_H
#define _LINUX_PCI_DMA_H

-#ifdef CONFIG_NEED_DMA_MAP_STATE
-#define DECLARE_PCI_UNMAP_ADDR(ADDR_NAME) dma_addr_t ADDR_NAME;
-#define DECLARE_PCI_UNMAP_LEN(LEN_NAME) __u32 LEN_NAME;
-#define pci_unmap_addr(PTR, ADDR_NAME) ((PTR)->ADDR_NAME)
-#define pci_unmap_addr_set(PTR, ADDR_NAME, VAL) (((PTR)->ADDR_NAME) = (VAL))
-#define pci_unmap_len(PTR, LEN_NAME) ((PTR)->LEN_NAME)
-#define pci_unmap_len_set(PTR, LEN_NAME, VAL) (((PTR)->LEN_NAME) = (VAL))
-#else
-#define DECLARE_PCI_UNMAP_ADDR(ADDR_NAME)
-#define DECLARE_PCI_UNMAP_LEN(LEN_NAME)
-#define pci_unmap_addr(PTR, ADDR_NAME) (0)
-#define pci_unmap_addr_set(PTR, ADDR_NAME, VAL) do { } while (0)
-#define pci_unmap_len(PTR, LEN_NAME) (0)
-#define pci_unmap_len_set(PTR, LEN_NAME, VAL) do { } while (0)
-#endif
+#define DECLARE_PCI_UNMAP_ADDR(ADDR_NAME) DEFINE_DMA_UNMAP_ADDR(ADDR_NAME);
+#define DECLARE_PCI_UNMAP_LEN(LEN_NAME) DEFINE_DMA_UNMAP_LEN(LEN_NAME);
+#define pci_unmap_addr dma_unmap_addr
+#define pci_unmap_addr_set dma_unmap_addr_set
+#define pci_unmap_len dma_unmap_len
+#define pci_unmap_len_set dma_unmap_len_set

#endif
--
1.5.6.5

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