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staging: comedi: adl_pci9118: eliminate DMA buffer defragmentation step

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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: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2014-11-27 11:37:19 +00:00 committed by Greg Kroah-Hartman
parent bb4a51a1b5
commit e87f65b238
1 changed files with 46 additions and 21 deletions
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67
drivers/staging/comedi/drivers/adl_pci9118.c
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@ -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,
struct comedi_subdevice *s,
unsigned short *dma_buffer,
unsigned int num_samples)
static void move_block_from_dma(struct comedi_device *dev,
struct comedi_subdevice *s,
unsigned short *dma_buffer,
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)