Subject: [PATCH V2 6/8] dmaengine: bcm2835: move controlblock chain generation into separate method

From: [email-masked] (Vinod Koul)
Date: Wed, 13 Jan 2016 18:53:33 +0530

On Thu, Jan 07, 2016 at 05:33:04PM +0000, kernel at martin.sperl.org wrote:

> +static inline bool bcm2835_dma_is_lite(struct bcm2835_chan *c)
> +{
> +	/* dma channels >= 7 are LITE channels */
> +	return (c->ch >= 7);

Why not DT data here as well

> +}
> +
> +static inline size_t bcm2835_dma_max_frame_length(struct bcm2835_chan *c)
> +{
> +	/* lite and normal channels have different max frame length */
> +	return bcm2835_dma_is_lite(c) ? MAX_LITE_DMA_LEN : MAX_DMA_LEN;

Or rather get length from DT..

> +static struct bcm2835_desc *bcm2835_dma_create_cb_chain(
> +	struct dma_chan *chan, enum dma_transfer_direction direction,
> +	bool cyclic, u32 info, u32 finalextrainfo, size_t frames,
> +	dma_addr_t src, dma_addr_t dst, size_t buf_len,
> +	size_t period_len, gfp_t gfp)
> +{
> +	struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
> +	size_t len = buf_len, total_len;
> +	size_t frame;
> +	struct bcm2835_desc *d;
> +	struct bcm2835_cb_entry *cb_entry;
> +	struct bcm2835_dma_cb *control_block;
> +	size_t max_len = bcm2835_dma_max_frame_length(c);
> +
> +	/* allocate and setup the descriptor. */
> +	d = kzalloc(sizeof(*d) + frames * sizeof(struct bcm2835_cb_entry),
> +		    gfp);

odd style.. btw should flag be GFP_NOWAIT ..?

> +		/* fill in the control block */
> +		control_block = cb_entry->cb;
> +		control_block->info = info;
> +		control_block->src = src;
> +		control_block->dst = dst;
> +		if (buf_len) {
> +			control_block->length = min(max_len, len);
> +			if (period_len &&
> +			    (total_len + control_block->length >=
> +			     period_len)) {
> +				/* set to end of period_len */
> +				control_block->length =
> +					period_len - total_len;
> +				/* add extrainfo when cyclic */
> +				if (cyclic)
> +					control_block->info |=
> +						finalextrainfo;
> +				/* and reset total_len */
> +				total_len = 0;
> +			}

this looks hard to read, perhpas a helper will make it look better

> +	/* the last frame requires extra flags */
> +	d->cb_list[d->frames - 1].cb->info |= finalextrainfo;
> +
> +	/* check the size - if there is some missmatch,
> +	 * then this is detected here
> +	 */

this is not kernel style for multi-line comments

>  	/* Grab configuration */
>  	if (!is_slave_direction(direction)) {
> -		dev_err(chan->device->dev, "%s: bad direction?\n", __func__);
> +		dev_err(chan->device->dev,
> +			"%s: bad direction?\n", __func__);

unrelated change

> -	/* Now allocate and setup the descriptor. */
> -	d = kzalloc(sizeof(*d), GFP_NOWAIT);
> -	if (!d)
> -		return NULL;
> +	/* warn if buf_len is not a multiple of period_lenas this may leed
> +	 * to unexpected latencies for interrupts and thus audiable clicks
> +	 */

here too

>  	/*
> -	 * Iterate over all frames, create a control block
> -	 * for each frame and link them together.
> +	 * allocate the CB chain
> +	 * note that we need to use GFP_ATOMIC, as the ALSA i2s dmaengine

dmaengine drivers use GFP_NOWAIT in these cases

-- 
~Vinod