Messages in this thread | | | Date | Mon, 6 Feb 2012 00:22:13 +0800 | Subject | Re: [PATCH resent v2 1/2] ioport : add DEFINE_RES_DMA_SIZE_NAMED macro | From | Huang Shijie <> |
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On Sun, Feb 5, 2012 at 8:34 PM, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > On Sun, Feb 05, 2012 at 07:53:31PM +0800, Huang Shijie wrote: >> Does any one have any comments about this patch? > > Yes. Having a flat numberspace for DMAs invites the same problems that > we have with the flat IRQ numberspace when it comes to having multiple > DMA controllers. > > With DMA engine drivers, channels are allocated using a match function > and unspecified match data. While a linear numberspace can be used, > that sets itself up for clashing between different DMA controllers > especially if the numberspace overlaps. > > What's missing from this patch set is an illustration of how this will > be used. > > Another issue here is that having the peripheral drivers know about the > exact match function and what data the DMA engines require ties the > periperal drivers to their respective DMA engine. One of the points of > DMA engine is to separate that knowledge, so that the same peripheral IP > can be re-used with different DMA engines. > > To encode knowledge of the DMA engine into the peripheral driver basically > destroys the purpose of having a DMA engine API. > > So, I believe that _if_ we are going down the path of using the DMA engine > API for our SoCs, we really don't want to invent a linear DMA numberspace > by putting DMA numbers into resources.
ok. thanks.
Huang Shijie -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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