Subject: Re: [PATCH RFC v12 3/7] dma: mpc512x: add support for peripheral transfers

From: Vinod Koul <[email-masked]>
Date: Fri, 2 May 2014 22:33:33 +0530

On Wed, Apr 23, 2014 at 05:53:25PM +0400, Alexander Popov wrote:
> Introduce support for slave s/g transfer preparation and the associated
> device control callback in the MPC512x DMA controller driver, which adds
> support for data transfers between memory and peripheral I/O to the
> previously supported mem-to-mem transfers.
> 
> Signed-off-by: Alexander Popov <[email-masked]>
> ---
>  drivers/dma/mpc512x_dma.c | 239 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 234 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/mpc512x_dma.c b/drivers/dma/mpc512x_dma.c
> index 0b17f4d..ca2fe03 100644
> --- a/drivers/dma/mpc512x_dma.c
> +++ b/drivers/dma/mpc512x_dma.c
> @@ -2,6 +2,7 @@
>   * Copyright (C) Freescale Semicondutor, Inc. 2007, 2008.
>   * Copyright (C) Semihalf 2009
>   * Copyright (C) Ilya Yanok, Emcraft Systems 2010
> + * Copyright (C) Alexander Popov, Promcontroller 2014
>   *
>   * Written by Piotr Ziecik <[email-masked]>. Hardware description
>   * (defines, structures and comments) was taken from MPC5121 DMA driver
> @@ -29,8 +30,17 @@
>   */
>  
>  /*
> - * This is initial version of MPC5121 DMA driver. Only memory to memory
> - * transfers are supported (tested using dmatest module).
> + * MPC512x and MPC8308 DMA driver. It supports
> + * memory to memory data transfers (tested using dmatest module) and
> + * data transfers between memory and peripheral I/O memory
> + * by means of slave s/g with these limitations:
> + *  - chunked transfers (transfers with more than one part) are refused
> + *     as long as proper support for scatter/gather is missing;
> + *  - transfers on MPC8308 always start from software as this SoC appears
> + *     not to have external request lines for peripheral flow control;
> + *  - minimal memory <-> I/O memory transfer chunk is 4 bytes and consequently
> + *     source and destination addresses must be 4-byte aligned
> + *     and transfer size must be aligned on (4 * maxburst) boundary;
>   */
>  
>  #include <linux/module.h>
> @@ -189,6 +199,7 @@ struct mpc_dma_desc {
>  	dma_addr_t			tcd_paddr;
>  	int				error;
>  	struct list_head		node;
> +	int				will_access_peripheral;
>  };
>  
>  struct mpc_dma_chan {
> @@ -201,6 +212,12 @@ struct mpc_dma_chan {
>  	struct mpc_dma_tcd		*tcd;
>  	dma_addr_t			tcd_paddr;
>  
> +	/* Settings for access to peripheral FIFO */
> +	dma_addr_t			src_per_paddr;
> +	u32				src_tcd_nunits;
> +	dma_addr_t			dst_per_paddr;
> +	u32				dst_tcd_nunits;
> +
>  	/* Lock for this structure */
>  	spinlock_t			lock;
>  };
> @@ -251,8 +268,23 @@ static void mpc_dma_execute(struct mpc_dma_chan *mchan)
>  	struct mpc_dma_desc *mdesc;
>  	int cid = mchan->chan.chan_id;
>  
> -	/* Move all queued descriptors to active list */
> -	list_splice_tail_init(&mchan->queued, &mchan->active);
> +	while (!list_empty(&mchan->queued)) {
> +		mdesc = list_first_entry(&mchan->queued,
> +						struct mpc_dma_desc, node);
> +		/*
> +		 * Grab either several mem-to-mem transfer descriptors
> +		 * or one peripheral transfer descriptor,
> +		 * don't mix mem-to-mem and peripheral transfer descriptors
> +		 * within the same 'active' list.
> +		 */
> +		if (mdesc->will_access_peripheral) {
> +			if (list_empty(&mchan->active))
> +				list_move_tail(&mdesc->node, &mchan->active);
> +			break;
> +		} else {
> +			list_move_tail(&mdesc->node, &mchan->active);
> +		}
> +	}
>  
>  	/* Chain descriptors into one transaction */
>  	list_for_each_entry(mdesc, &mchan->active, node) {
> @@ -278,7 +310,17 @@ static void mpc_dma_execute(struct mpc_dma_chan *mchan)
>  
>  	if (first != prev)
>  		mdma->tcd[cid].e_sg = 1;
> -	out_8(&mdma->regs->dmassrt, cid);
> +
> +	if (mdma->is_mpc8308) {
> +		/* MPC8308, no request lines, software initiated start */
> +		out_8(&mdma->regs->dmassrt, cid);
> +	} else if (first->will_access_peripheral) {
> +		/* Peripherals involved, start by external request signal */
> +		out_8(&mdma->regs->dmaserq, cid);
> +	} else {
> +		/* Memory to memory transfer, software initiated start */
> +		out_8(&mdma->regs->dmassrt, cid);
> +	}
>  }
>  
>  /* Handle interrupt on one half of DMA controller (32 channels) */
> @@ -596,6 +638,7 @@ mpc_dma_prep_memcpy(struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
>  	}
>  
>  	mdesc->error = 0;
> +	mdesc->will_access_peripheral = 0;
>  	tcd = mdesc->tcd;
>  
>  	/* Prepare Transfer Control Descriptor for this transaction */
> @@ -643,6 +686,189 @@ mpc_dma_prep_memcpy(struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
>  	return &mdesc->desc;
>  }
>  
> +static struct dma_async_tx_descriptor *
> +mpc_dma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
> +		unsigned int sg_len, enum dma_transfer_direction direction,
> +		unsigned long flags, void *context)
> +{
> +	struct mpc_dma *mdma = dma_chan_to_mpc_dma(chan);
> +	struct mpc_dma_chan *mchan = dma_chan_to_mpc_dma_chan(chan);
> +	struct mpc_dma_desc *mdesc = NULL;
> +	dma_addr_t per_paddr;
> +	u32 tcd_nunits;
> +	struct mpc_dma_tcd *tcd;
> +	unsigned long iflags;
> +	struct scatterlist *sg;
> +	size_t len;
> +	int iter, i;
> +
> +	/* Currently there is no proper support for scatter/gather */
Why? Is this HW or SW limitation?

> +	if (sg_len != 1)
> +		return NULL;
> +
> +	if (!is_slave_direction(direction))
> +		return NULL;
> +
> +	for_each_sg(sgl, sg, sg_len, i) {
Then this doesn't make sense...

> +		spin_lock_irqsave(&mchan->lock, iflags);
> +
> +		mdesc = list_first_entry(&mchan->free,
> +						struct mpc_dma_desc, node);
> +		if (!mdesc) {
> +			spin_unlock_irqrestore(&mchan->lock, iflags);
> +			/* Try to free completed descriptors */
> +			mpc_dma_process_completed(mdma);
> +			return NULL;
> +		}
> +
> +		list_del(&mdesc->node);
> +
> +		if (direction == DMA_DEV_TO_MEM) {
> +			per_paddr = mchan->src_per_paddr;
> +			tcd_nunits = mchan->src_tcd_nunits;
> +		} else {
> +			per_paddr = mchan->dst_per_paddr;
> +			tcd_nunits = mchan->dst_tcd_nunits;
> +		}
> +
> +		spin_unlock_irqrestore(&mchan->lock, iflags);
> +
> +		if (per_paddr == 0 || tcd_nunits == 0)
> +			goto err_prep;
> +
> +		mdesc->error = 0;
> +		mdesc->will_access_peripheral = 1;
> +
> +		/* Prepare Transfer Control Descriptor for this transaction */
> +		tcd = mdesc->tcd;
> +
> +		memset(tcd, 0, sizeof(struct mpc_dma_tcd));
> +
> +		if (!IS_ALIGNED(sg_dma_address(sg), 4))
> +			goto err_prep;
> +
> +		if (direction == DMA_DEV_TO_MEM) {
> +			tcd->saddr = per_paddr;
> +			tcd->daddr = sg_dma_address(sg);
> +			tcd->soff = 0;
> +			tcd->doff = 4;
what are these?

> +		} else {
> +			tcd->saddr = sg_dma_address(sg);
> +			tcd->daddr = per_paddr;
> +			tcd->soff = 4;
> +			tcd->doff = 0;
> +		}
> +
> +		tcd->ssize = MPC_DMA_TSIZE_4;
> +		tcd->dsize = MPC_DMA_TSIZE_4;
> +
> +		len = sg_dma_len(sg);
> +		tcd->nbytes = tcd_nunits * 4;
> +		if (!IS_ALIGNED(len, tcd->nbytes))
> +			goto err_prep;
> +
> +		iter = len / tcd->nbytes;
> +		if (iter >= 1 << 15) {
> +			/* len is too big */
> +			goto err_prep;
> +		}
> +		/* citer_linkch contains the high bits of iter */
> +		tcd->biter = iter & 0x1ff;
> +		tcd->biter_linkch = iter >> 9;
> +		tcd->citer = tcd->biter;
> +		tcd->citer_linkch = tcd->biter_linkch;
> +
> +		tcd->e_sg = 0;
> +		tcd->d_req = 1;
> +
> +		/* Place descriptor in prepared list */
> +		spin_lock_irqsave(&mchan->lock, iflags);
> +		list_add_tail(&mdesc->node, &mchan->prepared);
> +		spin_unlock_irqrestore(&mchan->lock, iflags);
> +	}
> +
> +	return &mdesc->desc;
> +
> +err_prep:
> +	/* Put the descriptor back */
> +	spin_lock_irqsave(&mchan->lock, iflags);
> +	list_add_tail(&mdesc->node, &mchan->free);
> +	spin_unlock_irqrestore(&mchan->lock, iflags);
> +
> +	return NULL;
> +}
> +
> +static int mpc_dma_device_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
> +							unsigned long arg)
> +{
> +	struct mpc_dma_chan *mchan;
> +	struct mpc_dma *mdma;
> +	struct dma_slave_config *cfg;
> +	unsigned long flags;
> +
> +	mchan = dma_chan_to_mpc_dma_chan(chan);
> +	switch (cmd) {
> +	case DMA_TERMINATE_ALL:
> +		/* Disable channel requests */
> +		mdma = dma_chan_to_mpc_dma(chan);
> +
> +		spin_lock_irqsave(&mchan->lock, flags);
> +
> +		out_8(&mdma->regs->dmacerq, chan->chan_id);
> +		list_splice_tail_init(&mchan->prepared, &mchan->free);
> +		list_splice_tail_init(&mchan->queued, &mchan->free);
> +		list_splice_tail_init(&mchan->active, &mchan->free);
> +
> +		spin_unlock_irqrestore(&mchan->lock, flags);
> +
> +		return 0;
empty line after this pls

> +	case DMA_SLAVE_CONFIG:
> +		/*
> +		 * Constraints:
> +		 *  - only transfers between a peripheral device and
> +		 *     memory are supported;
> +		 *  - minimal transfer chunk is 4 bytes and consequently
> +		 *     source and destination addresses must be 4-byte aligned
> +		 *     and transfer size must be aligned on (4 * maxburst)
> +		 *     boundary;
> +		 *  - during the transfer RAM address is being incremented by
> +		 *     the size of minimal transfer chunk;
> +		 *  - peripheral port's address is constant during the transfer.
> +		 */
> +
> +		cfg = (void *)arg;
> +
> +		if (cfg->src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES ||
> +		    cfg->dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES ||
and why this limtation, doesnt seem covered above?

> +		    !IS_ALIGNED(cfg->src_addr, 4) ||
> +		    !IS_ALIGNED(cfg->dst_addr, 4)) {
> +			return -EINVAL;
> +		}
> +
> +		spin_lock_irqsave(&mchan->lock, flags);
> +
> +		mchan->src_per_paddr = cfg->src_addr;
> +		mchan->src_tcd_nunits = cfg->src_maxburst;
> +		mchan->dst_per_paddr = cfg->dst_addr;
> +		mchan->dst_tcd_nunits = cfg->dst_maxburst;
> +
> +		/* Apply defaults */
> +		if (mchan->src_tcd_nunits == 0)
> +			mchan->src_tcd_nunits = 1;
> +		if (mchan->dst_tcd_nunits == 0)
> +			mchan->dst_tcd_nunits = 1;
> +
> +		spin_unlock_irqrestore(&mchan->lock, flags);
> +
> +		return 0;
empty line here too

> +	default:
> +		/* Unknown command */
> +		break;
> +	}
> +
> +	return -ENXIO;
> +}
> +
>  static int mpc_dma_probe(struct platform_device *op)
>  {
>  	struct device_node *dn = op->dev.of_node;
> @@ -727,9 +953,12 @@ static int mpc_dma_probe(struct platform_device *op)
>  	dma->device_issue_pending = mpc_dma_issue_pending;
>  	dma->device_tx_status = mpc_dma_tx_status;
>  	dma->device_prep_dma_memcpy = mpc_dma_prep_memcpy;
> +	dma->device_prep_slave_sg = mpc_dma_prep_slave_sg;
> +	dma->device_control = mpc_dma_device_control;
>  
>  	INIT_LIST_HEAD(&dma->channels);
>  	dma_cap_set(DMA_MEMCPY, dma->cap_mask);
> +	dma_cap_set(DMA_SLAVE, dma->cap_mask);
>  
>  	for (i = 0; i < dma->chancnt; i++) {
>  		mchan = &mdma->channels[i];
> -- 
> 1.8.4.2
> 

-- 
~Vinod