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

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

(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.

(BTW, I would like to take this series through the Tegra tree to
simplify dependencies. So, I'm looking for ack's on the drivers rather
than for them to be applied. I had hoped Richard would point this out
when posting the patches)

> 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?