linux-kernel - Re: [PATCHv8 2/2] dma: Add Freescale eDMA engine driver support

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Message-ID: <5890639.zaOC7MRE09@wuerfel>
Date:	Wed, 08 Jan 2014 11:53:43 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Jingchang Lu <jingchang.lu@...escale.com>
Cc:	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCHv8 2/2] dma: Add Freescale eDMA engine driver support

On Wednesday 08 January 2014 10:24:38 Jingchang Lu wrote:

> > +- clocks : Phandle of the DMA channel group block clock of the eDMA
> > module
> > +- clock-names : The channel group block clock names

Turn these around and first define the required names, then state
that 'clocks' should contain none clock specifier for each clock
name.

> > +sai2: sai@...31000 {
> > +	compatible = "fsl,vf610-sai";
> > +	reg = <0x40031000 0x1000>;
> > +	interrupts = <0 86 0x04>;
> > +	clocks = <&clks VF610_CLK_SAI2>;
> > +	clock-names = "sai";
> > +	dma-names = "tx", "rx";
> > +	dmas = <&edma0 VF610_EDMA_DMAMUX0 VF610_EDMA0_MUX0_SAI2_TX>,
> > +		<&edma0 VF610_EDMA_DMAMUX0 VF610_EDMA0_MUX0_SAI2_RX>;
> > +	status = "disabled";
> > +};

It seems wrong to have macros defined like VF610_EDMA0_MUX0_SAI2_TX,
in particular in the example. These should just be literal numbers.

It's ok to have macros for the VF610_EDMA_DMAMUX0, but I suspect
that the possible values are just '0' and '1', which means a literal
would be just as easy here.

> > +struct fsl_edma_hw_tcd {
> > +	u32	saddr;
> > +	u16	soff;
> > +	u16	attr;
> > +	u32	nbytes;
> > +	u32	slast;
> > +	u32	daddr;
> > +	u16	doff;
> > +	u16	citer;
> > +	u32	dlast_sga;
> > +	u16	csr;
> > +	u16	biter;
> > +} __packed;

The structure is packed already, and marking it __packed
will just mean that the compiler can't access the members
atomically. Please remove the __packed keyword.

> > +/* bytes swapping according to eDMA controller's endian */
> > +#define EDMA_SWAP16(e, v)	(__force u16)(e->big_endian ?
> > cpu_to_be16(v) : cpu_to_le16(v))
> > +#define EDMA_SWAP32(e, v)	(__force u32)(e->big_endian ?
> > cpu_to_be32(v) : cpu_to_le32(v))

Maybe use inline functions for these?

> > +/*
> > + * copying of ARM read{b,w,l) and write{b,w,l) macro definations
> > + * except for doing default swap of cpu_to_le32, the bytes swap
> > + * is done depending on eDMA controller's endian defination,
> > + * which may be big-endian or little-endian.
> > + */
> > +static inline u16 edma_readw(void __iomem *addr)
> > +{
> > +	u16 __v = (__force u16) __raw_readw(addr);
> > +
> > +	__iormb();
> > +	return __v;
> > +}

The comment doesn't seem to match the implementation: You don't
actually do swaps here at all, which means this will fail when
your kernel is running in big-endian mode. Just use the regular
readw() etc, or use ioread16/ioread16be depending on the flag,
and get rid of your EDMA_SWAP macros.

No need to come up with your own scheme when the problem has
been solved already elsewhere.

> > +static irqreturn_t fsl_edma_irq_handler(int irq, void *dev_id)
> > +{
> > +	if (fsl_edma_tx_handler(irq, dev_id) == IRQ_HANDLED)
> > +		return IRQ_HANDLED;
> > +
> > +	return fsl_edma_err_handler(irq, dev_id);
> > +}

Does this do the right thing if both completion and error are
signalled at the same time? It seems you'd miss the error interrupt.

> > +static bool fsl_edma_filter_fn(struct dma_chan *chan, void *mux)
> > +{
> > +	 return (chan->chan_id / DMAMUX_NR) == (u32)mux;
> > +}
> > +
> > +static struct dma_chan *fsl_edma_xlate(struct of_phandle_args *dma_spec,
> > +		struct of_dma *ofdma)
> > +{
> > +	struct dma_chan *chan;
> > +	dma_cap_mask_t mask;
> > +
> > +	if (dma_spec->args_count != 2)
> > +		return NULL;
> > +
> > +	dma_cap_zero(mask);
> > +	dma_cap_set(DMA_SLAVE, mask);
> > +	dma_cap_set(DMA_CYCLIC, mask);
> > +	chan = dma_request_channel(mask, fsl_edma_filter_fn, (void
> > *)dma_spec->args[0]);
> > +	if (chan)
> > +		fsl_edma_chan_mux(to_fsl_edma_chan(chan), dma_spec->args[1],
> > true);
> > +	return chan;
> > +}

Please remove the filter function now and use dma_get_slave_chan
with the correct channel as an argument. No need to walk all
available channels in the system and introduce bugs by not
ignoring other dma engines.

	Arnd
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