On Mon, 25 Jun 2012, Arnd Bergmann wrote: [snip] > The channel data in the device tree is still in a format > that is specific to that dmaengine driver and interpreted > by it. Using the regular dma_filter_fn prototype is not > necessary, but it would be convenient because the dmaengine > code already knows how to deal with it. If we don't use this > method, how about adding another callback to struct dma_device > like > > bool (*device_match)(struct dma_chan *chan, struct property *req); I like this idea, but why don't we extend it to also cover the non-DT case? I.e., why don't we add the above callback (call it "match" or "filter" or anything else) to dmaengine operations and inside (the extended) dma_request_channel(), instead of calling the filter function, passed as a parameter, we loop over all registered DMAC devices and call their filter callbacks, until one of them returns true? In fact, it goes back to my earlier proposal from http://thread.gmane.org/gmane.linux.kernel/1246957 which I, possibly, failed to explain properly. So, the transformation chain from today's API would be (all code is approximate): (today) <client driver> dma_request_channel(mask, filter, filter_arg); <dmaengine_core> for_each_channel() { ret = (*filter)(chan, filter_arg); if (ret) { ret = chan->device->device_alloc_chan_resources(chan); if (!ret) return chan; else return NULL; } } (can be transformed to) <client driver> dma_request_channel(mask, filter_arg); <dmaengine_core> for_each_channel() { ret = chan->device->filter(chan, filter_arg); if (ret) { <same as above> } } (which further could be simplified to) <client driver> dma_request_channel(mask, filter_arg); <dmaengine_core> for_each_channel() { ret = chan->device->device_alloc_chan_resources(chan, filter_arg); if (!ret) return chan; else if (ret != -ENODEV) return ret; /* -ENODEV - try the next channel */ } Which is quite similar to my above mentioned proposal. Wouldn't this both improve the present API and prepare it for DT? Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
