[alsa-devel] of_dma_request_slave_channel() failed ?

[Kuninori Morimoto]

Hi Geert

> > ...which is in fact the exact same problem that the IOMMU code has -
> > might it make sense to give of_dma_request_slave_channel() similar
> > (optional?) driver_deferred_probe_check_state() logic, i.e. "if my DMAC
> > driver's not shown up by this point, assume it's not built-in and go on
> > without it". Of course it is somewhat easier for IOMMU drivers as
> > there's zero chance of those popping up as modules later on.
> 
> It may solve the issue in some cases.  But only if the dmac is reprobed
> before the DMA slave driver, which is not guaranteed.
> 
> BTW, it seems e.g. i2c and serial suffer from the same problem, and fall
> back to PIO. However, these drivers try to obtain the DMA channel when
> used, not during probe, so they start using DMA after the dmac has been
> probed successfully.

Actually sound driver get DMA channel when used.
But checking DMA availability when probe timing (= try to get, and release it soon).
sound driver side other approach is that it don't check it when probe.

Best regards
---
Kuninori Morimoto