Date: Sun, 29 Feb 2004 21:22:32 -0500 (EST) From: John Wehle <john@feith.com> To: scottl@freebsd.org Cc: multimedia@freebsd.org Subject: Re: FreeBSD 4.9 / 5.2 Hauppauge PVR-250 / 350 Driver Patch (Jan 31, 2004) Message-ID: <200403010222.i212MW801703@jwlab.FEITH.COM>
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> When you are allocating a buffer with bus_dmamem_alloc(),
> you don't need to check the return value of bus_dmamap_load()
> since it is guaranteed to succeed and not be deferred in that case.
So it's preferable to keep the code simple by just having a comment
in the driver indicating the call can't fail instead of being paranoid
and checking the return?
> Also, the dma tag for these buffers should be created with NULL,
> NULL for the lock arguments.
Why? You wouldn't by chance have a pointer to documentation for
bus_dma_tag_create which discusses the relevant issues?
> Also, you might be able to save the overhead of uiomove() by using
> bus_dmamap_load_uio() to operate directly on the uio buffers rather
> than pre-allocting static buffers.
The current design of using a ring buffer addresses the following concerns:
1) The data needs to be massaged by the driver prior to handing it off
to the application.
2) The buffer supplied by the application might not be large enough to
contain the entire frame (and the card requires an entire frame to
be transferred in one DMA operation at a time).
3) The card is capturing data in realtime and can't wait for resources
to become available.
Perhaps in the future further information on the card's capabilities will
become available allowing for a more optimal design.
> Anyways, very nice driver.
Thanks for the feedback.
-- John
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