How to use the DMA Engine in FreeBSD?

[Warner Losh]

On Thu, Dec 13, 2018, 3:04 AM Rajesh Kumar <rajfbsd at gmail.com wrote:

> Hi,
>
> Is there any good documentation available to understand the existing
> support, API's and how-to use the DMA Engine in FreeBSD?
>


Usually you just use pci busmastering and it just works.

I am trying to write a test driver which will use DMA Engine to do the data
> transfer (rather than plain memcpy which involves cpu).  Can anyone point
> to any driver implementation which has similar functions implemented?  I
> see references to SYS_RES_DRQ to allocate DMA channels and play around. But
> that seems to be specific to ISA. Can it be used for PCI drivers as well?
>

No. ISA DMA is only for really old hardware without it's own DMA engine.

Look at the busdma api/man page.

Warner

> Thanks,
> Rajesh.
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