linux-kernel - Re: [PATCH v4 1/8] dmaengine: of

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Date:	Thu, 9 Apr 2015 11:24:58 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
CC:	<vinod.koul@...el.com>, <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>, <arnd@...db.de>
Subject: Re: [PATCH v4 1/8] dmaengine: of_dma: Support for DMA routers

On 04/08/2015 06:42 PM, Maxime Ripard wrote:
>> ---
>>  Documentation/devicetree/bindings/dma/dma.txt | 28 +++++++++
>>  drivers/dma/dmaengine.c                       |  7 +++
>>  drivers/dma/of-dma.c                          | 86 +++++++++++++++++++++++++++
>>  include/linux/dmaengine.h                     | 17 ++++++
>>  include/linux/of_dma.h                        | 21 +++++++
>>  5 files changed, 159 insertions(+)
> 
> Can that be moved to a header / C file of its own?
> 
> There's a lot of various code already in dmaengine.h and dmaengine.c,
> it would be really great to avoid adding more random stuff in there.

This patch adds the core support for DMA signal routers. It adds fairly small
amount of generic code to the core to achieve this. I don't think it would be
better to create let's say of-dma-router.c and .h just for this and export
functions from of-dma.c to be used outside of the file.

>> +	chan = ofdma_target->of_dma_xlate(&dma_spec_target, ofdma_target);
>> +	if (chan) {
>> +		chan->router = ofdma->dma_router;
>> +		chan->route_data = route_data;
>> +	} else {
>> +		ofdma->dma_router->route_free(ofdma->dma_router->dev, route_data);
> 
> This line is over 80 characters.

Oh, true.

>> +int of_dma_router_register(struct device_node *np,
>> +			   void *(*of_dma_route_allocate)
>> +			   (struct of_phandle_args *, struct of_dma *),
>> +			   struct dma_router *dma_router)
>> +{
>> +	struct of_dma	*ofdma;
>> +
>> +	if (!np || !of_dma_route_allocate || !dma_router) {
>> +		pr_err("%s: not enough information provided\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>> +	ofdma = kzalloc(sizeof(*ofdma), GFP_KERNEL);
>> +	if (!ofdma)
>> +		return -ENOMEM;
> 
> Is that expected that you allocate through kzalloc, but never have a
> matching free function implemented?

The free is via the of_dma_router_free() in case the router is removed
runtime, which is unlikely to happen since it will cause all DMA request to fail.

>> diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
>> index 56bc026c143f..734e449f87c1 100644
>> --- a/include/linux/of_dma.h
>> +++ b/include/linux/of_dma.h
>> @@ -23,6 +23,9 @@ struct of_dma {
>>  	struct device_node	*of_node;
>>  	struct dma_chan		*(*of_dma_xlate)
>>  				(struct of_phandle_args *, struct of_dma *);
>> +	void			*(*of_dma_route_allocate)
>> +				(struct of_phandle_args *, struct of_dma *);
>> +	struct dma_router	*dma_router;
> 
> I don't really see why this is really tied to the device tree.

The signal router is not a DMA device, it is represented in the device tree
and the code will do the needed translation, which is transparent for the DMA
clients and also for the DMA controllers. Neither should know about the signal
router.
Similar translation can be done for ACPI.

> Couldn't we use the device_alloc_chan_resources to do that?

Not really. The router itself is not a DMA controller. The routing need to be
configured before the device_alloc_chan_resources can be called for the real
DMA controller. The signal router (core part + the HW driver) need to prepare
the route and do the translation so the filter function of the DMA driver can
validate the translated request.

-- 
Péter
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