From: Edward Estabrook <[EMAIL PROTECTED]>
Here is a patch updating the Userspace IO documentation to
detail support to dynamically allocate and use coherent DMA
from userspace. This patch applies against 2.6.28-rc6.
The gist of this implementation is to overload uio's mmap
functionality to allocate
and map a new DMA region on demand. The bus-specific DMA address as returned by
dma_alloc_coherent() is made available to userspace in the 1st long
word of the newly
created region (as well as through the conventional 'addr' file in sysfs).
The kernel-api change is that passing an offset value of 0xFFFFF000UL to a uio
device's mmap() operation will dynamically allocate a DMA region. This cannot
break existing code as the previous UIO code only allowed a maximum of 5
mappings.
To allocate a DMA region you use the following:
/* Pass this magic number to mmap as offset to
* dynamically allocate a chunk of memory */
#define DMA_MEM_ALLOCATE_MMAP_OFFSET 0xFFFFF000UL
void* memory = mmap (NULL, size, PROT_READ | PROT_WRITE , MAP_SHARED,
fd, DMA_MEM_ALLOCATE_MMAP_OFFSET);
u_int64_t *addr = *(u_int64_t *) memory;
where 'size' is the size in bytes of the region you want and fd is the
opened /dev/uioN file.
Allocation occurs in page sized pieces by design to ensure that
buffers are page-aligned.
Memory is released when the uio_unregister_device() is called.
Signed-off-by: Edward Estabrook <[EMAIL PROTECTED]>
---
--- linux-2.6.28-rc6/Documentation/DocBook/uio-howto.tmpl.orig 2008-12-03
12:03:43.000000000 -0800
+++ linux-2.6.28-rc6/Documentation/DocBook/uio-howto.tmpl 2008-12-03
13:11:53.000000000 -0800
@@ -42,6 +42,12 @@ GPL version 2.
<revhistory>
<revision>
+ <revnumber>0.6</revnumber>
+ <date>2008-12-03</date>
+ <authorinitials>ee</authorinitials>
+ <revremark>Added description of DMA control.</revremark>
+ </revision>
+ <revision>
<revnumber>0.5</revnumber>
<date>2008-05-22</date>
<authorinitials>hjk</authorinitials>
@@ -284,11 +290,17 @@ interested in translating it, please ema
require access to more than one PCI memory region in a driver.
</para>
<para>
+ Each UIO device can also dynamically allocate coherent DMA
+ memory regions and map these to userspace. Once created they
+ can be mapped like any other UIO memory region.
+</para>
+<para>
Each mapping has its own directory in sysfs, the first mapping
appears as <filename>/sys/class/uio/uioX/maps/map0/</filename>.
Subsequent mappings create directories <filename>map1/</filename>,
- <filename>map2/</filename>, and so on. These directories will only
- appear if the size of the mapping is not 0.
+ <filename>map2/</filename>, and so on. These directories will
+ appear even if the size of the mapping is 0 to accommodate dynamically
+ created DMA mappings.
</para>
<para>
Each <filename>mapX/</filename> directory contains two read-only files
@@ -318,6 +330,24 @@ interested in translating it, please ema
offset = N * getpagesize();
</programlisting>
+<para>
+ From userspace a DMA region may be dynamically allocated and mapped
+ via the <function>mmap()</function> call by specifying the size of the
+ region in bytes in the <varname>length</varname> parameter and setting
+ <varname>offset = 0xFFFFF000</varname>.
+</para>
+<para>
+ The bus-specific DMA address as required to configure hardware DMA
+ registers will be stored in the first long word of the resulting mapped
+ region.
+</para>
+<programlisting format="linespecific">
+#define DMA_MEM_ALLOCATE_MMAP_OFFSET 0xFFFFF000UL
+void* memory = mmap (NULL, size, PROT_READ | PROT_WRITE , MAP_SHARED,
+ fd, DMA_MEM_ALLOCATE_MMAP_OFFSET);
+u_int64_t *addr = *(u_int64_t *) memory;
+</programlisting>
+
</sect1>
</chapter>
@@ -572,6 +602,50 @@ to set up sysfs files for this mapping.
</para>
</sect1>
+<sect1 id="dma_region_mmap">
+<title>Allocating DMA region with mmap()</title>
+ <para>
+ To allocate and map a DMA memory region you use
+ use <function>mmap()</function>. You may create as
+ many regions as system resources allow by repeated use of
+ <function>mmap()</function>.
+ </para>
+ <para>
+ Specify the size of the desired region, in bytes, in the
+ <varname>length</varname> parameter and set
+ <varname>offset = 0xFFFFF000</varname>. The region size will
+ be rounded up to a multiple of page size to ensure proper
+ alignment.
+ </para>
+ <para>
+ The bus-specific DMA address is stored in the first long word of the
+ resulting mapped region. The newly assigned memory index N is
+ returned in the second long word of the resulting mapped region. This
+ index is only required if the userspace driver needs to unmap and
+ then later remap the DMA region as the single call to
+ <function>mmap()</function> is sufficient to both allocate and map the
+ region.
+ </para>
+ <para>
+ Since every memory mapping has its own directory in sysfs
+ <filename>/sys/class/uio/uioX/maps/mapN/</filename> will be created
+ where N is the dynamically generated index of the mapping just
+ allocated.
+ </para>
+ <para>
+ Dynamically allocated DMA regions remain available for use
+ until <function>uio_unregister_device()</function> is called, at
+ which point the memory is released.
+ </para>
+<programlisting format="linespecific">
+ #define DMA_MEM_ALLOCATE_MMAP_OFFSET 0xFFFFF000UL
+ void* memory = mmap (NULL, size, PROT_READ | PROT_WRITE , MAP_SHARED,
+ fd, DMA_MEM_ALLOCATE_MMAP_OFFSET);
+ u_int64_t *addr = *(u_int64_t *) memory;
+</programlisting>
+
+</sect1>
+
<sect1 id="wait_for_interrupts">
<title>Waiting for interrupts</title>
<para>
@@ -583,7 +657,7 @@ to set up sysfs files for this mapping.
attention because an error occured.
</para>
<para>
- <filename>/dev/uioX</filename> is a read-only file. A
+ <filename>/dev/uioX</filename> is a read-write file. A
<function>read()</function> will always block until an
interrupt occurs. There is only one legal value for the
<varname>count</varname> parameter of
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