linux-kernel - Re: [PATCH v2 4/9] dmaengine: st_fdma: Add STMicroelectronics FDMA engine driver support

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Message-ID: <20150929102320.GD16955@griffinp-ThinkPad-X1-Carbon-2nd>
Date:	Tue, 29 Sep 2015 11:23:20 +0100
From:	Peter Griffin <peter.griffin@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	srinivas.kandagatla@...il.com, maxime.coquelin@...com,
	patrice.chotard@...com, vinod.koul@...el.com, lee.jones@...aro.org,
	robh+dt@...nel.org, dmaengine@...r.kernel.org,
	devicetree@...r.kernel.org, Ludovic Barre <ludovic.barre@...com>
Subject: Re: [PATCH v2 4/9] dmaengine: st_fdma: Add STMicroelectronics FDMA
 engine driver support

Hi Arnd,

Thanks for reviewing.

On Fri, 11 Sep 2015, Arnd Bergmann wrote:

> On Friday 11 September 2015 15:14:26 Peter Griffin wrote:
> > +
> > +#include "st_fdma.h"
> 
> Just move the contents of that file here, no other driver should
> be including it.

There is another file st_fdma_xbar.c which will be upstreamed shortly
which uses some parts of this header. It was originally part of the
v1 series here: -
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/355069.html

But I removed it from subsequent submissions as it needs to be re-worked
to use some of the new xbar functionality recently added by TI.

However large parts probably aren't required by xbar, and could be
moved into the c file, so I will move those parts in the next submission.

> 
> > +static struct dma_chan *st_fdma_of_xlate(struct of_phandle_args *dma_spec,
> > +					 struct of_dma *ofdma)
> > +{
> > +	struct st_fdma_dev *fdev = ofdma->of_dma_data;
> > +	struct st_fdma_cfg cfg;
> > +
> > +	if (dma_spec->args_count < 1)
> > +		return NULL;
> > +
> > +	cfg.of_node = dma_spec->np;
> > +	cfg.req_line = dma_spec->args[0];
> > +	cfg.req_ctrl = 0;
> > +	cfg.type = ST_FDMA_TYPE_FREE_RUN;
> > +
> > +	if (dma_spec->args_count > 1)
> > +		cfg.req_ctrl = dma_spec->args[1] & REQ_CTRL_CFG_MASK;
> > +
> > +	if (dma_spec->args_count > 2)
> > +		cfg.type = dma_spec->args[2];
> 
> The binding mandates #dma-cells=<3>, so you can just return an error
> otherwise.

Ok will fix in next submission
> 
> > +	dev_dbg(fdev->dev, "xlate req_line:%d type:%d req_ctrl:%#x\n",
> > +		cfg.req_line, cfg.type, cfg.req_ctrl);
> > +
> > +	return dma_request_channel(fdev->dma_device.cap_mask,
> > +			st_fdma_filter_fn, &cfg);
> > +}
> 
> Why this indirection? You should be able to just use
> dma_get_any_slave_channel() to get the first available channel and
> then configure it the same way that the filter function does.

Ok I will look at using this API instead of dma_request_channel
in the next submission.

> 
> > +bool st_fdma_filter_fn(struct dma_chan *chan, void *param)
> > +{
> > +	struct st_fdma_cfg *config = param;
> > +	struct st_fdma_chan *fchan = to_st_fdma_chan(chan);
> > +
> > +	if (!param)
> > +		return false;
> > +
> > +	if (fchan->fdev->dma_device.dev->of_node != config->of_node)
> > +		return false;
> > +
> > +	fchan->cfg = *config;
> > +
> > +	return true;
> > +}
> 
> Please drop this until there is a board file that references the
> function. Otherwise it's just dead code. I assume there are some
> users in arch/sh/ in a private tree?

I'll drop this in the next submission. There aren't any users I can
see in the private tree. This function is currently only used by
dma_reuest_channel above, so won't be required if we move over to
using dma_get_any_slave_channel().

regards,

Peter.
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