Re: [PATCH RFC v6 4/5] dma: mpc512x: register for device tree channel lookup

[Gerhard Sittig <gsi-ynQEQJNshbs@public.gmane.org>]

[ dropping devicetree, we're DMA specific here ]

On Tue, Dec 24, 2013 at 16:06 +0400, Alexander Popov wrote:
> 
> --- a/drivers/dma/mpc512x_dma.c
> +++ b/drivers/dma/mpc512x_dma.c
> [ ... ]
> @@ -950,6 +951,7 @@ static int mpc_dma_probe(struct platform_device *op)
>  	INIT_LIST_HEAD(&dma->channels);
>  	dma_cap_set(DMA_MEMCPY, dma->cap_mask);
>  	dma_cap_set(DMA_SLAVE, dma->cap_mask);
> +	dma_cap_set(DMA_PRIVATE, dma->cap_mask);
>  
>  	for (i = 0; i < dma->chancnt; i++) {
>  		mchan = &mdma->channels[i];

What are the implications of this?  Is a comment due?

I haven't found documentation about the DMA_PRIVATE flag, only
saw commit 59b5ec21446b9 "dmaengine: introduce
dma_request_channel and private channels".  Alex, unless I'm
missing something this one-line change is quite a change in
semantics, and has dramatic influence on the code's behaviour
(ignores the DMA controller when looking for channels that can do
mem-to-mem transfers).

Please reason about this change some more, and explain what it
does and why it's needed.  Consider the fact that this driver
handles both MPC5121 as well as MPC8308 hardware.


virtually yours
Gerhard Sittig
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