Messages in this thread | | | Date | Sun, 31 Jul 2011 00:32:55 +0200 | Subject | Re: [PATCH 04/18] dmaengine/amba-pl08x: Remove redundant comment and rewrite original | From | Linus Walleij <> |
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2011/7/29 viresh kumar <viresh.linux@gmail.com>: > On 7/29/11, Koul, Vinod <vinod.koul@intel.com> wrote: >> On Fri, 2011-07-29 at 16:19 +0530, Viresh Kumar wrote: >>> /* >>> - * Autoselect a master bus to use for the transfer this prefers the >>> - * destination bus if both available if fixed address on one bus the >>> - * other will be chosen >>> + * Autoselect a master bus to use for the transfer >>> + * - prefers the destination bus if both available >>> + * - if fixed address on one bus the other will be chosen >> Not sure I get it, English is not my first language :) > > Nor mine either. :) > > Will give some more explanation. > > But before that i wanted to know the exact purpose of this > master-slave concept here.
The PL08x has two bus mastering interfaces. They can be connected to two separate busses and two adress spaces even, usually that is not the case though.
> Probably it is for choosing the victim for reduction of width, in case > src and dest addresses > are misaligned to each other. > @Russell and Linus: Is this correct?
You can see from the function that it is only about choosing the master and slave. One of them is reading from some memory and one of them is writing. These are called source and destination respectively.
What it then does is:
- If one of the buses will be targeting a fixed address, choose the other one, so the one that increase address become master and the fixed address slave . - If both buses increas address (usually memory-to-memory) the third case is activated and deals with trying to set the widest bus as master.
Crystal clear?
Please copyedit/author something like the above...
Thanks, Linus Walleij -- 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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