On 05/27/2015 10:48 AM, Arnaud Pouliquen wrote: [...]
+static int sti_platform_engine_probe(struct platform_device *pdev) +{
- /*
* Driver can not use snd_dmaengine_pcm_register.* Reason is that DMA needs to load a firmware.* This firmware is loaded on request_channel from file system.* So can not be done in probe while alsa card enumerated before* file system is mounted*/This is not the only driver with similar needs, the Intel drivers use firmwares as well (all the DMA is done by the DSP which needs firmware) and even if it were we should be able to arrange for this to work rather than having to open code things. That might mean having the dmaengine driver requesting firmware with _nowait() and then waiting until the firmware appears before registering as a DMA controller for example. We may also be able to have the DMA engine only load the firmware when it's used rather than at probe (that might allow us to keep the DMA controller powered off for longer which would be a power win if possible).
It's not just restricted to audio either.
Move dmaengine_pcm_request_chan from register to open could be a good compromise with (i hope) no impact on drivers that already use soc_generic_dma_engine. This is the implementation already proposed in of pcm_dmaengine.c Another issue i'm facing, is that i have one DMA channel per CPU_DAI instance. As simple card imposes to define CPU_DAIs in one platform device, i need to define specific DMA name per CPU_DAI. What is your recommendation on this point: Do you want that i use snd_dmaengine_pcm_register and propose soc_gebneric_dmaengine driver patches? or simply reuse pcm_dmaengine helper functions as much as possible.
You really want to request the DMA channels in the probe callback of the driver (and also use the the generic-dmaengine-pcm driver). This makes sure that you have proper support for probe deferral, etc. The DMA driver should probably not request the firmware inside the channel_request() callback. As Mark sad this will not only affect audio, but all usecases that involve DMAengine.
Btw. what is the DMA driver you are using, is it already upstream?
- Lars