linux-kernel - Re: [PATCH v2 3/7] dmaengine: Add driver for TI DMA crossbar on DRA7x

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Date:	Thu, 26 Mar 2015 14:31:30 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	<tony@...mide.com>, <linux@....linux.org.uk>,
	<grant.likely@...aro.org>, <dmaengine@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <robh+dt@...nel.org>,
	<nm@...com>
Subject: Re: [PATCH v2 3/7] dmaengine: Add driver for TI DMA crossbar on DRA7x

On 03/26/2015 12:56 PM, Vinod Koul wrote:
>> +#define TI_XBAR_OUTPUTS	127
>> +#define TI_XBAR_INPUTS	256
> Ideally this should be moved to DT. Will next revision of this chip always
> support these output and inputs?

They are coming from DT. I'm using these as fall back values in case we can
not get this from DT and a warning will be printed in case if this unlikely
event happens.

>> +
>> +static DEFINE_IDR(map_idr);
>> +
>> +struct ti_dma_xbar_data {
>> +	struct dma_router dmarouter;
>> +	struct regmap *regmap;
>> +
>> +	uint safe_val; /* Value to rest the crossbar lines */
>> +	uint xbar_requests; /* number of DMA requests connected to XBAR */
>> +	uint dma_requests; /* number of DMA requests forwarded to DMA */
>> +
>> +	void __iomem *iomem;
>> +};
>> +
>> +struct ti_dma_xbar_map {
>> +	int xbar_in;
>> +	int xbar_out;
>> +};
>> +
>> +static void ti_dma_xbar_free(struct device *dev, void *route_data)
>> +{
>> +	struct ti_dma_xbar_data *xbar = dev_get_drvdata(dev);
>> +	struct ti_dma_xbar_map *map = route_data;
>> +
>> +	dev_dbg(dev, "Unmapping XBAR%d (was routed to %d)\n",
>> +		map->xbar_in, map->xbar_out);
>> +
>> +	regmap_write(xbar->regmap, map->xbar_out * 2, 0);
> just out of curiosity how much do you save using regmap :)

good point, not much I guess. I had it implemented w/o regmap as well, but
thought why not use regmap if it is available.

>> +static int ti_dma_xbar_probe(struct platform_device *pdev)
>> +{
>> +	struct device_node *node = pdev->dev.of_node;
>> +	struct device_node *dma_node;
>> +	struct ti_dma_xbar_data *xbar;
>> +	struct resource *res;
>> +	void __iomem *iomem;
>> +	int i, ret;
>> +
>> +	if (!node)
>> +		return -ENODEV;
>> +
>> +	dma_node = of_parse_phandle(node, "dma-device", 0);
>> +	if (!dma_node) {
>> +		dev_err(&pdev->dev, "Can't get target DMA node\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	xbar = devm_kzalloc(&pdev->dev, sizeof(*xbar), GFP_KERNEL);
>> +	if (!xbar)
>> +		return -ENOMEM;
>> +
>> +	if (of_property_read_u32(dma_node, "dma-requests",
>> +				 &xbar->dma_requests)) {
>> +		dev_info(&pdev->dev,
>> +			 "Missing XBAR output information, using %u.\n",
>> +			 TI_XBAR_OUTPUTS);
>> +		xbar->dma_requests = TI_XBAR_OUTPUTS;
>> +	}
>> +	of_node_put(dma_node);
> _put here?

The code takes the real dma controller's node and it should be put back after
I have got the information I needed from it (number of DMA requests).

> 
>> +int omap_dmaxbar_init(void)
>> +{
>> +	return platform_driver_register(&ti_dma_xbar_driver);
>> +}
>> +arch_initcall(omap_dmaxbar_init);
> why arch_initcall?

It should be on the same init level as the real DMA controller. omap-dma at
the moment, but in some platforms this can work with the edma as well.
Since all device in the system (well most of them anyway) uses DMA it is
better to not delay their probe with deferring because the crossbar driver is
still not loaded

-- 
Péter
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