Commit e87f65b2 authored by Ian Abbott's avatar Ian Abbott Committed by Greg Kroah-Hartman
Browse files

staging: comedi: adl_pci9118: eliminate DMA buffer defragmentation step 



The DMA operations used by the driver may have been set up to acquire
data from unwanted channels in addition to the wanted channels.
Currently, `interrupt_pci9118_ai_dma()` calls `defragment_dma_buffer()`
to move all the wanted data to the start of the DMA buffer and then
calls `comedi_buf_write_samples()` to copy it all to the comedi async
buffer.  Those two functions used to be called from
`move_block_from_dma()` which was absorbed into
`interrupt_pci9118_ai_dma()`.

Reinstate `move_block_from_dma()` but rewrite it to copy data directly
from the wanted fragments of the DMA buffer to the comedi async buffer
without defragmenting the buffer first.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent bb4a51a1

drivers/staging/comedi/drivers/adl_pci9118.c

+46 −21
Original line number Diff line number Diff line
@@ -502,29 +502,56 @@ static unsigned int valid_samples_in_act_dma_buf(struct comedi_device *dev, 
	return n_samples;

}



static unsigned int defragment_dma_buffer(struct comedi_device *dev,

static void move_block_from_dma(struct comedi_device *dev,

				struct comedi_subdevice *s,

				unsigned short *dma_buffer,

					  unsigned int num_samples)

				unsigned int n_raw_samples)

{

	struct pci9118_private *devpriv = dev->private;

	struct comedi_cmd *cmd = &s->async->cmd;

	unsigned int i = 0, j = 0;

	unsigned int start_pos = devpriv->ai_add_front,

	    stop_pos = devpriv->ai_add_front + cmd->chanlist_len;

	unsigned int raw_scanlen = devpriv->ai_add_front + cmd->chanlist_len +

	    devpriv->ai_add_back;

	unsigned int start_pos = devpriv->ai_add_front;

	unsigned int stop_pos = start_pos + cmd->chanlist_len;

	unsigned int span_len = stop_pos + devpriv->ai_add_back;

	unsigned int dma_pos = devpriv->ai_act_dmapos;

	unsigned int x;



	for (i = 0; i < num_samples; i++) {

		if (devpriv->ai_act_dmapos >= start_pos &&

		    devpriv->ai_act_dmapos < stop_pos) {

			dma_buffer[j++] = dma_buffer[i];

	if (span_len == cmd->chanlist_len) {

		/* All samples are to be copied. */

		comedi_buf_write_samples(s, dma_buffer, n_raw_samples);

		dma_pos += n_raw_samples;

	} else {

		/*

		 * Not all samples are to be copied.  Buffer contents consist

		 * of a possibly non-whole number of spans and a region of

		 * each span is to be copied.

		 */

		while (n_raw_samples) {

			if (dma_pos < start_pos) {

				/* Skip samples before start position. */

				x = start_pos - dma_pos;

				if (x > n_raw_samples)

					x = n_raw_samples;

				dma_pos += x;

				n_raw_samples -= x;

				if (!n_raw_samples)

					break;

			}

			if (dma_pos < stop_pos) {

				/* Copy samples before stop position. */

				x = stop_pos - dma_pos;

				if (x > n_raw_samples)

					x = n_raw_samples;

				comedi_buf_write_samples(s, dma_buffer, x);

				dma_pos += x;

				n_raw_samples -= x;

			}

			/* Advance to next span. */

			start_pos += span_len;

			stop_pos += span_len;

		}

		devpriv->ai_act_dmapos++;

		devpriv->ai_act_dmapos %= raw_scanlen;

	}



	return j;

	/* Update position in span for next time. */

	devpriv->ai_act_dmapos = dma_pos % span_len;

}



static void pci9118_exttrg_enable(struct comedi_device *dev, bool enable)
@@ -681,10 +708,8 @@ static void interrupt_pci9118_ai_dma(struct comedi_device *dev, 
		}

	}



	if (n_all) {

		n_valid = defragment_dma_buffer(dev, s, dmabuf->virt, n_all);

		comedi_buf_write_samples(s, dmabuf->virt, n_valid);

	}

	if (n_all)

		move_block_from_dma(dev, s, dmabuf->virt, n_all);



	if (!devpriv->ai_neverending) {

		if (s->async->scans_done >= cmd->stop_arg)