linux-kernel - Re: [PATCH v2 06/53] dmaengine: Create a generic dma_slave

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Date:	Thu, 16 Oct 2014 18:24:53 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Antoine Ténart <antoine@...e-electrons.com>,
	lars@...afoo.de, Russell King <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 06/53] dmaengine: Create a generic dma_slave_caps
 callback

On Thu, Oct 16, 2014 at 07:15:40PM +0300, Laurent Pinchart wrote:
> Hi Maxime,
> 
> Thank you for the patch.
> 
> On Thursday 16 October 2014 12:17:05 Maxime Ripard wrote:
> > dma_slave_caps is very important to the generic layers that might interact
> > with dmaengine, such as ASoC. Unfortunately, it has been added as yet
> > another dma_device callback, and most of the existing drivers haven't
> > implemented it, reducing its reliability.
> > 
> > Introduce a generic behaviour and a flag to trigger it. In case this flag
> > hasn't been set, fall back to the old mechanism.
> > 
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> > ---
> >  include/linux/dmaengine.h | 25 +++++++++++++++++++++----
> >  1 file changed, 21 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index 4d0294ec3567..85afd71df2e7 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -643,6 +643,8 @@ struct dma_device {
> >  	int dev_id;
> >  	struct device *dev;
> > 
> > +	bool generic_slave_caps;
> > +
> >  	int (*device_alloc_chan_resources)(struct dma_chan *chan);
> >  	void (*device_free_chan_resources)(struct dma_chan *chan);
> > 
> > @@ -772,17 +774,32 @@ static inline struct dma_async_tx_descriptor
> > *dmaengine_prep_interleaved_dma(
> > 
> >  static inline int dma_get_slave_caps(struct dma_chan *chan, struct
> > dma_slave_caps *caps) {
> 
> This is getting too big for an inline function, it should be moved to 
> drivers/dma/dmaengine.c.

I agree, but I wanted to do that in another patch set. This one is
just getting bigger and bigger, and this is not really the point of
this serie.

> > +	struct dma_device *device;
> > +
> >  	if (!chan || !caps)
> >  		return -EINVAL;
> > 
> > +	device = chan->device;
> > +
> >  	/* check if the channel supports slave transactions */
> > -	if (!test_bit(DMA_SLAVE, chan->device->cap_mask.bits))
> > +	if (!test_bit(DMA_SLAVE, device->cap_mask.bits))
> > +		return -ENXIO;
> > +
> > +	if (device->device_slave_caps)
> > +		return device->device_slave_caps(chan, caps);
> > +
> > +	/*
> > +	 * Check whether it reports it uses the generic slave
> > +	 * capabilities, if not, that means it doesn't support any
> > +	 * kind of slave capabilities reporting.
> > +	 */
> > +	if (device->generic_slave_caps)
> >  		return -ENXIO;
> 
> Couldn't we replace that check with if (device->device_control) and get rid of 
> the generic_slave_caps field ? Drivers converted to the new API would then get 
> slave caps support for free.

Not really. Drivers might have converted to the splitted
device_control (and actually all of them are), while they don't define
the values needed to implement properly the generic slave caps
retrieval (and the vast majority of them doesn't).

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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