Messages in this thread | | | From | Rabin Vincent <> | Date | Sun, 14 Apr 2013 18:34:51 +0200 | Subject | Re: [PATCH 4/8] dmaengine: ste_dma40: Do not configure channels during an channel allocation |
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2013/4/12 Lee Jones <lee.jones@linaro.org>: > So I need to devise another way, as this function cannot be called > here either. Using the dmaengine API, allocating a channel and > configuring it are to be completed using different calls. Using the > API correctly, there is no way the driver can setup the channel > with all of the relevant information during allocation time. > > The steps are as follows: > > dma_request_channel() - here we only allot a channel number and > allocate the appropriate resources for the > channel. > > dma_slave_config() - this is where we're meant to configure the > channel, so d40_config_write() needs to be > called here, as only dma_slave_config() will > carry the information required so as > d40_*_cfg() can make the correct decisions.
The choice between whether a physical or a logical channel is used is not something that is configurable via dma_slave_config(). And d40_config_write() only needs that information, and that information is available in dma_request_channel(). Therefore no more information relevant to d40_config_write() will be obtained in dma_slave_config(). Hence d40_config_write() can be called in dma_request_channel().
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