Re: [PATCH 6/9] serial: tegra: move to generic dma DT binding

[Richard Zhao <rizhao@nvidia.com>]

On Wed, Jul 31, 2013 at 12:46:42AM +0800, Stephen Warren wrote:
> On 07/29/2013 09:31 PM, Richard Zhao wrote:
> > On Sat, Jul 27, 2013 at 03:39:15AM +0800, Stephen Warren wrote:
> >> On 07/23/2013 10:09 PM, Richard Zhao wrote:
> >>> - driver: remove use of nvidia,dma-request-selector
> >>> 	  use dma_request_slave_channel to request channel
> >>> - update binding doc
> >>
> >> This patch needs to be amended so that the DMA channel is looked up
> >> during probe() rather than open(), to guarantee that deferred probe
> >> works. It's possible to hold off probe, but not possible AFAIK to hold
> >> off opening the port.
> >
> > How about avoid return -EPROBE_DEFER at open() time? It can be in
> > another patch.
> 
> I don't really understand what you mean. -EPROBE_DEFER is something that
> only makes sense for probe() to return (or functions used by probe()).
> It doesn't make sense to return it anywhere else, since probe deferral
> is something that can only happen for probe().
What I meant is, it might not worth to move request channel to probe
only because we need to check error and return -EPROBE_DEFER.

dma_request_slave_channel is better to be called as late as possible to
make better dynamic use of dma channels.

Actually, I searched the kernel code, most drivers don't return EPROBE_DEFER
when dma_request_slave_channel failed. dma_request_slave_channel can
fail in many cases, and dma device not probed is only one case.

Thanks
Richard