Re: correct use of bus_dmamap_sync

From: Dinesh Nair (dinesh_at_alphaque.com)
Date: 10/25/05

  • Next message: Dinesh Nair: "Re: correct use of bus_dmamap_sync" 
    Date: Wed, 26 Oct 2005 02:46:36 +0800
To: John Baldwin <jhb@freebsd.org>

    On 10/26/05 01:27 John Baldwin said the following:
    > On Tuesday 25 October 2005 09:15 am, Dinesh Nair wrote:
    >>(must i malloc space for them before passing them into those functions, or
    >>will the call to bus_dmamem_alloc do it for me ?)
    >
    > bus_dmamem_alloc() will do it for you.

    thanx.

    > Probably not as the sync()'s don't really do anything with memory allocated
    > via bus_dmamem_alloc(). The operations are named from the CPU's perspective,

    however, the man page at
    http://www.freebsd.org/cgi/man.cgi?query=bus_dmamap_sync&apropos=0&sektion=0&manpath=FreeBSD+5.4-stable&format=html
    says,

    "Although no explicit loading is required to access the memory referenced
    by the returned map, the synchronization requirements as described in the
    bus_dmamap_sync() section still apply."

    also, is bus_dmamap_load() required, since the same man page section above
    says it isnt ?

    have things changed between freebsd 4.x (which i'm using) and freebsd 5.x ?

    > thus when you send data to your device, that is a WRITE operation (even
    > though your device is doing a DMA to read data), and when you get data back
    > from your device, that is a READ operation (even though your device is doing
    > a DMA to write the data into the buffer).

    thanx, the verbiage on the man page is slightly confusing with it's use of
    CPU, giving the opposite impression. 

    -- 
Regards,                           /\_/\   "All dogs go to heaven."
dinesh@alphaque.com                (0 0)    http://www.alphaque.com/
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