Date: Sun, 11 Feb 2007 15:07:53 -0600 From: Jason Harmening <jason.harmening@gmail.com> To: freebsd-doc@freebsd.org, freebsd-drivers@freebsd.org Subject: Inconsistency in bus_dma manpage? Message-ID: <200702111507.53789.jason.harmening@gmail.com>
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In the busdma_sync_op_t section of the bus_dma manpage, the sync operations
are described as follows:
BUS_DMASYNC_PREREAD Perform any synchronization required
prior to an update of host memory by the
DMA read operation.
BUS_DMASYNC_PREWRITE Perform any synchronization required
after an update of host memory by the CPU
and prior to DMA write operations.
BUS_DMASYNC_POSTREAD Perform any synchronization required
after DMA read operations and prior to
CPU access to host memory.
BUS_DMASYNC_POSTWRITE Perform any synchronization required
after DMA write operations.
Makes sense...But in the section describing bus_dmamap_load, the following
example is given:
For example,
the CPU might be used to setup the contents of a buffer that is
to be DMA'ed into a device. To ensure that the data are visible
via the device's mapping of that memory, the buffer must be
loaded and a dma sync operation of BUS_DMASYNC_PREREAD must be
performed.
I believe the example is incorrect--it's actually describing the case where
BUS_DMASYNC_PREWRITE would be necessary.
Thanks,
Jason Harmening
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