Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH 1/2] dma: of: Add generic xlate function for matching by channel id | Date | Tue, 9 Apr 2013 15:06:02 +0200 |
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On Tuesday 09 April 2013, Lars-Peter Clausen wrote: > On 04/09/2013 01:28 PM, Vinod Koul wrote: > > On Sat, Mar 30, 2013 at 09:38:54AM +0100, Lars-Peter Clausen wrote: > >> On 03/29/2013 10:49 PM, Vinod Koul wrote: > >>> On Mon, Mar 25, 2013 at 02:16:51PM +0100, Lars-Peter Clausen wrote: > >>>> This patch adds a new generic of dma xlate callback function which will match a > >>>> channel by its id. > >>> how will the client know which "id" to request? > >> > >> The devicetree tells it, or what exactly do you mean? > > Is this global id? Anrd, what does the id mean in DT? > > It's more or less a device specific cookie. And in this case we are using a > 1 to 1 mapping to the channel number.
To clarify this some more: The slave driver uses a name that is defined in the binding of for the slave device to request a specific channel. This is typically something trivial like "rx" or "data" that defines how the slave driver knows its channel.
This gets passed to the dmaengine core, which looks up a dmaengine driver specific description of a channel, using the name and the slave device pointer as keys. Normally this is just a request number, sometimes it can be a combinattion of request number with some other data like a master number or the DMA direction, if the dmaengine driver requires that information in order to allocate the channel.
In this specific case, it is the chan_id number, which is correct for any driver that uses the same number for slave_id and chan_id. It may be an exaggeration to call it "generic", since this only works for a few dmaengine drivers, but it's reasonable to have this kind of helper in common code since there are multiple drivers with the same characteristic.
Arnd
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