Subject: Re: Valid use of bus_dma(9)?
To: David Young <>
From: Jochen Kunz <>
List: tech-kern
Date: 07/24/2004 00:33:08
On Fri, 23 Jul 2004 15:38:09 -0500
David Young <> wrote:

> Network drivers don't copy ds_addr into transmit/receive descriptors?
> How does this work if they are not "system physical addresses" ?
Copying ds_addr into a DMA descriptor / register is a valid use, because
the value is read only from ds_addr. But fpa(4) _modifies_ ds_addr and
feeds that back to other bus_dma(9) functions. ds_addr is only the
interface to the client code (device driver). The actual mapping
information may be stored in other, hidden MD fields of a
bus_dma_segment_t. I.e. bus_dma(9) _may_ use ds_addr in a write only