staging: comedi: pcl816: fix short DMA transactions

When the cmd->stop_src == TRIG_COUNT the last DMA transfer might be smaller
than the buffer size. This results in invalid data being added to the async
buffer.

Add a 'size' member to the DMA descriptor and initialize it with the
actual size of the DMA transfer. Use that in interrupt and ai subdevice
(*poll) function to return the proper number of samples. Use the
comedi_bytes_to_samples() helper to convert the byte size to comedi
samples in the interrupt handler.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/pcl816.c b/drivers/staging/comedi/drivers/pcl816.c
index 1b76085..f880cb9 100644 (file)
--- a/drivers/staging/comedi/drivers/pcl816.c
+++ b/drivers/staging/comedi/drivers/pcl816.c
@@ -116,6 +116,7 @@ static const struct pcl816_board boardtypes[] = {
 struct pcl816_dma_desc {
        void *virt_addr;        /* virtual address of DMA buffer */
        dma_addr_t hw_addr;     /* hardware (bus) address of DMA buffer */
+       unsigned int size;      /* transfer size (in bytes) */
 };
 
 struct pcl816_private {
@@ -158,30 +159,30 @@ static void pcl816_ai_setup_dma(struct comedi_device *dev,
        struct pcl816_dma_desc *dma = &devpriv->dma_desc[0];
        struct comedi_cmd *cmd = &s->async->cmd;
        unsigned int dma_flags;
-       unsigned int bytes;
 
-       bytes = devpriv->hwdmasize;
        if (cmd->stop_src == TRIG_COUNT) {
                /*  how many */
-               bytes = cmd->stop_arg * comedi_bytes_per_scan(s);
+               dma->size = cmd->stop_arg * comedi_bytes_per_scan(s);
 
                /*  how many DMA pages we must fill */
-               devpriv->dma_runs_to_end = bytes / devpriv->hwdmasize;
+               devpriv->dma_runs_to_end = dma->size / devpriv->hwdmasize;
 
                /* on last dma transfer must be moved */
-               devpriv->last_dma_run = bytes % devpriv->hwdmasize;
+               devpriv->last_dma_run = dma->size % devpriv->hwdmasize;
                devpriv->dma_runs_to_end--;
                if (devpriv->dma_runs_to_end >= 0)
-                       bytes = devpriv->hwdmasize;
-       } else
+                       dma->size = devpriv->hwdmasize;
+       } else {
+               dma->size = devpriv->hwdmasize;
                devpriv->dma_runs_to_end = -1;
+       }
 
        devpriv->cur_dma = 0;
        set_dma_mode(devpriv->dma, DMA_MODE_READ);
        dma_flags = claim_dma_lock();
        clear_dma_ff(devpriv->dma);
        set_dma_addr(devpriv->dma, dma->hw_addr);
-       set_dma_count(devpriv->dma, bytes);
+       set_dma_count(devpriv->dma, dma->size);
        release_dma_lock(dma_flags);
        enable_dma(devpriv->dma);
 }
@@ -199,13 +200,14 @@ static void pcl816_ai_setup_next_dma(struct comedi_device *dev,
                /* switch dma bufs */
                devpriv->cur_dma = 1 - devpriv->cur_dma;
                dma = &devpriv->dma_desc[devpriv->cur_dma];
+               if (devpriv->dma_runs_to_end)
+                       dma->size = devpriv->hwdmasize;
+               else
+                       dma->size = devpriv->last_dma_run;
                set_dma_mode(devpriv->dma, DMA_MODE_READ);
                dma_flags = claim_dma_lock();
                set_dma_addr(devpriv->dma, dma->hw_addr);
-               if (devpriv->dma_runs_to_end)
-                       set_dma_count(devpriv->dma, devpriv->hwdmasize);
-               else
-                       set_dma_count(devpriv->dma, devpriv->last_dma_run);
+               set_dma_count(devpriv->dma, dma->size);
                release_dma_lock(dma_flags);
                enable_dma(devpriv->dma);
        }
@@ -324,8 +326,8 @@ static irqreturn_t pcl816_interrupt(int irq, void *d)
        struct comedi_subdevice *s = dev->read_subdev;
        struct pcl816_private *devpriv = dev->private;
        struct pcl816_dma_desc *dma = &devpriv->dma_desc[devpriv->cur_dma];
+       unsigned int nsamples;
        unsigned int bufptr;
-       unsigned int len;
 
        if (!dev->attached || !devpriv->ai_cmd_running) {
                pcl816_ai_clear_eoc(dev);
@@ -340,11 +342,11 @@ static irqreturn_t pcl816_interrupt(int irq, void *d)
 
        pcl816_ai_setup_next_dma(dev, s);
 
-       len = (devpriv->hwdmasize >> 1) - devpriv->ai_poll_ptr;
+       nsamples = comedi_bytes_to_samples(s, dma->size) - devpriv->ai_poll_ptr;
        bufptr = devpriv->ai_poll_ptr;
        devpriv->ai_poll_ptr = 0;
 
-       transfer_from_dma_buf(dev, s, dma->virt_addr, bufptr, len);
+       transfer_from_dma_buf(dev, s, dma->virt_addr, bufptr, nsamples);
 
        pcl816_ai_clear_eoc(dev);
 
@@ -542,7 +544,7 @@ static int pcl816_ai_poll(struct comedi_device *dev, struct comedi_subdevice *s)
        }
 
        /*  where is now DMA in buffer */
-       top1 = devpriv->hwdmasize - top1;
+       top1 = dma->size - top1;
        top1 >>= 1;             /*  sample position */
        top2 = top1 - devpriv->ai_poll_ptr;
        if (top2 < 1) {         /*  no new samples */