lkml.org 
[lkml]   [1999]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: Address spaces on a i386 - Getting Confused
Date
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Generator" CONTENT="MS Exchange Server version 5.5.2448.0">
<TITLE>RE: Address spaces on a i386 - Getting Confused</TITLE>
</HEAD>
<BODY>

<P><FONT SIZE=2>&gt; </FONT>
<BR><FONT SIZE=2>&gt; &gt; As a future problem, some user-space pages will not be reachable by</FONT>
<BR><FONT SIZE=2>&gt; &gt; DMA anyway, because they are outside the bus address range of the</FONT>
<BR><FONT SIZE=2>&gt; &gt; device doing DMA.&nbsp; (cf. 32-bit PCI cards on &gt;4GB memory machines, or</FONT>
<BR><FONT SIZE=2>&gt; &gt; complexities of multi-bus machines).</FONT>
<BR><FONT SIZE=2>&gt; </FONT>
<BR><FONT SIZE=2>&gt; Indeed, and this is one of the problems I'll have to deal with for the</FONT>
<BR><FONT SIZE=2>&gt; large memory support.&nbsp; IO bounce buffers will be necessary, but that</FONT>
<BR><FONT SIZE=2>&gt; will be entirely transparent above the block device request layer.</FONT>
<BR><FONT SIZE=2>&gt; </FONT>
</P>

<P><FONT SIZE=2>How about a dmamalloc() function?&nbsp; Such a beast exists under systems like VxWorks.&nbsp; It guarantees not only that all memory allocated will be hardware addressable, but that it will be page aligned (so no offsets need to be computed when doing scatter/gather lists).&nbsp; The buffers could be allocated internally with it, and devices that are going to do streaming I/O could just allocate their memory using this call instead of malloc().</FONT></P>

<P><FONT SIZE=2>--</FONT>
<BR><FONT SIZE=2>Eric Lowe</FONT>
<BR><FONT SIZE=2>elowe@systran.com</FONT>
<BR><FONT SIZE=2>Software Engineer Co-op, Systran Corporation</FONT>
<BR><FONT SIZE=2>937-252-5601 x330</FONT>
<BR><FONT SIZE=2>((sorry for the HTML, my e-mail gateway is adding it, I can't disable it..))</FONT>
</P>

</BODY>
</HTML>
\
 
 \ /
  Last update: 2005-03-22 13:51    [W:0.079 / U:0.888 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site