Inconsistency in bus_dma manpage?
Jason Harmening
jason.harmening at gmail.com
Sun Feb 11 21:36:37 UTC 2007
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
More information about the freebsd-doc
mailing list