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Message-ID: <208aa0f00812032053w5efb99dbk94511b0f8c1f0925@mail.gmail.com> Date: Wed, 3 Dec 2008 20:53:27 -0800 From: "Edward Estabrook" <edward.estabrook.lkml@...il.com> To: linux-kernel@...r.kernel.org Cc: linux-api@...r.kernel.org, "Greg KH" <gregkh@...e.de>, hjk@...utronix.de, edward_estabrook@...lent.com Subject: [PATCH 1/1] Userspace I/O (UIO): Documentatin for userspace DMA support From: Edward Estabrook <Edward_Estabrook@...lent.com> 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 <Edward_Estabrook@...lent.com> --- --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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