Date: Tue, 29 May 2007 12:04:34 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: freebsd-current@freebsd.org Subject: PAT_WRITE_COMBINING: how to use? Message-ID: <18012.20265.657576.944142@grasshopper.cs.duke.edu>
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I would very much like to obtain a write-combine mapping of PCIe device memory for mxge(4) without depending on the flakiness of MTRRs. I currently use bus_alloc_resource() to map my device's memory space, and then use mem_range_attr_set() to attempt to change the memory to be write-combine. I recently noticed that pmap_mapdev_attr() function on amd64 & i386, but it looks like nexus_activate_resource() just calls pmap_mapdev(), which defaults to PAT_UNCACHEABLE. Would it be possible to add a flag which could tell the bus_* functions to map the memory write-combine? Or should I avoid bus_alloc_resource(), and map my device myself with pmap_mapdev_attr()? Or should I replace my call to mem_range_attr_set() with a call to pmap_change_attr? Thanks, Drew
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