Re: [PATCH 2/9] dma: tegra20-apbdma: move to generic device tree bindings

[Richard Zhao <rizhao-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On Wed, Jul 31, 2013 at 12:44:18AM +0800, Stephen Warren wrote:
> On 07/29/2013 09:06 PM, Richard Zhao wrote:
> > On Sat, Jul 27, 2013 at 03:27:58AM +0800, Stephen Warren wrote:
> >> (Stripping the Cc list a lot)
> >>
> >> On 07/23/2013 10:09 PM, Richard Zhao wrote:
> >>> Update tegra20-apbdma driver to adopt generic DMA device tree bindings.
> >>> It calls of_dma_controller_register() with of_dma_simple_xlate to get
> >>> the generic DMA device tree helper support. The #dma-cells for apbdma
> >>> must be 1, which is slave ID.
> >>>
> >>> The existing nvidia,dma-request-selector still works there, and the
> >>> support will be removed after all clients get converted to generic DMA
> >>> device tree helper.
> 
> >>> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> >>
> >>> +static bool tegra_dma_filter_fn(struct dma_chan *dc, void *param)
> >>> +{
> >>> +	if (dc->device->dev->driver == &tegra_dmac_driver.driver) {
> >>> +		struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> >>> +		unsigned req = *(unsigned *)param;
> >>> +
> >>> +		tdc->slave_id = req;
> >>> +
> >>> +		return true;
> >>> +	}
> >>> +	return false;
> >>> +}
> >>> +
> >>> +static struct of_dma_filter_info tegra_dma_info = {
> >>> +	.filter_fn = tegra_dma_filter_fn,
> >>> +};
> >>
> >> Why does this driver need to define a filter function? I thought the
> >> dmaengine's DT support would already match DMA clients/engines based on
> >> the phandle in DT? Isn't the need to pass the slave channel ID into
> >> drivers something pretty fundamental to dmaengine, and hence something
> >> it already supports?
> >
> > of_dma_simple_xlate only pass slave id to filter function. It needs
> > change to pass dt node too. I didn't start work on the common code
> > change yet. Do you think we need to hold it until common code change?
> 
> Oh dear, I can't see how the core DT DMA support can work for anyone
> without the ability to limit DMA clients to the specific DMA controller
> that's specified in DT. If that functionality truly is missing, then it
> certainly needs to be added first.

omap-dma uses the same way.