Messages in this thread | | | Date | Thu, 22 May 2014 16:56:18 +0100 | From | Srinivas Kandagatla <> | Subject | Re: [PATCH] dmaengine: qcom_bam_dma: Add descriptor flag APIs |
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On 22/05/14 16:32, Andy Gross wrote: > On Thu, May 22, 2014 at 04:27:05PM +0100, Srinivas Kandagatla wrote: > > <snip> > >>> >>> The EOT is not used for every transaction. It is part of a handshaking >>> protocol with the attached peripheral, much like the NWD (notify when done). As >>> near as I can tell today, no peripheral depends on the EOB, so we could drop it >>> for now until it is needed and cross this bridge when we need to. >> >> As EOT behaviour is totally dependent on the attached peripheral(or >> channel), Can't we make this specific to channel by passing >> additional flags in the DT dma channel descriptors? This will be >> better abstraction for drivers as well. > > Even for channels where you want to use EOT, you don't use it for every > transaction. So a global channel flag isn't going to work. This is the same > for NWD. It is a per descriptor choice.
Thanks Andy for explaining, I got it now. > >> >> I know that EOT flag is part of descriptor but still some channels >> *must* have EOT to run there state-machine correctly. So making it >> optional for those channels might be wrong. >> >> Are there any use cases for particular *channel* where EOT >> requirement changes dynamically? > > I2C is one example. You place EOT on the last transaction that makes up a > write/read transaction. You may have multiple descriptors to send data, but the > last one has EOT. And for read transactions, you place NWD on the last read > transaction. > > <snip> >
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