Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver | Date | Thu, 8 Sep 2011 18:19:29 +0200 |
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On Thursday 08 September 2011, Barry Song wrote: > i am not sure whether i have other way to require a special channel > for a special device. it seems dma_request_channel only gives me a > chance to use a filter function since my all channels have same DMA > cap masks. > > this filter is used by all drivers with DMA since every dma channel is > fixed to be assigned to one device. > > i did do some copy from coh901318.c: > bool coh901318_filter_id(struct dma_chan *chan, void *chan_id) > { > unsigned int ch_nr = (unsigned int) chan_id; > > if (ch_nr == to_coh901318_chan(chan)->id) > return true; > > return false; > } > EXPORT_SYMBOL(coh901318_filter_id); > > if it does become a common filter, we might have a function like: > > bool dmaengine_filter_match_channel_id(struct dma_chan *chan, void *chan_id) > { > if (ch_nr == chan->chan_id) > return true; > > return false; > } > EXPORT_SYMBOL(dmaengine_filter_match_channel_id);
Ok, I see now. I think it would be best to introduce a generic 'filter by device tree property' function or alternatively an dma_of_request_channel function like this:
struct dma_chan *dma_of_request_channel(struct device *dev, unsigned int index) { struct dma_device *dmadev; struct { unsigned int phandle; unsigned int channel_num; } *property; int lenp;
property = of_get_property(dev->of_node, "dma-channel", &lenp); if (lenp < (index * sizeof (*property)) return -EINVAL;
property += index;
dmadev = dma_find_device(of_find_node_by_phandle(property->phandle)); if (!dmadev) return -ENODEV;
return dma_get_channel(dmadev, property->channel_num); }
This way, you can link a device to its dma_channel in the device tree without the device driver even understanding what a dma_device or a channel id is.
Arnd
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