staging: comedi: rtd520: add a few comments

H Hartley Sweeten's recent series of patches to clean up the rtd520
driver made some of the register accesses harder to understand.  Add a
few comments to provide some clues to the reader.

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

diff --git a/drivers/staging/comedi/drivers/rtd520.c b/drivers/staging/comedi/drivers/rtd520.c
index 5a2953e9d9003fde9f5656ca6d5b0862b959ec0e..9998d6b25d2e04221044e85e1f0792538202c312 100644 (file)
--- a/drivers/staging/comedi/drivers/rtd520.c
+++ b/drivers/staging/comedi/drivers/rtd520.c
@@ -494,6 +494,7 @@ static int rtd520_probe_fifo_depth(struct comedi_device *dev)
 
        writel(0, devpriv->las0 + LAS0_ADC_FIFO_CLEAR);
        rtd_load_channelgain_list(dev, 1, &chanspec);
+       /* ADC conversion trigger source: SOFTWARE */
        writel(0, devpriv->las0 + LAS0_ADC_CONVERSION);
        /* convert  samples */
        for (i = 0; i < limit; ++i) {
@@ -544,7 +545,7 @@ static int rtd_ai_rinsn(struct comedi_device *dev,
        /* write channel to multiplexer and clear channel gain table */
        rtd_load_channelgain_list(dev, 1, &insn->chanspec);
 
-       /* set conversion source */
+       /* ADC conversion trigger source: SOFTWARE */
        writel(0, devpriv->las0 + LAS0_ADC_CONVERSION);
 
        /* convert n samples */
@@ -908,8 +909,9 @@ abortTransfer:
        /* fall into transferDone */
 
 transferDone:
+       /* pacer stop source: SOFTWARE */
        writel(0, devpriv->las0 + LAS0_PACER_STOP);
-       writel(0, devpriv->las0 + LAS0_PACER);
+       writel(0, devpriv->las0 + LAS0_PACER);  /* stop pacer */
        writel(0, devpriv->las0 + LAS0_ADC_CONVERSION);
        devpriv->intMask = 0;
        writew(devpriv->intMask, devpriv->las0 + LAS0_IT);
@@ -1180,8 +1182,9 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
        int timer;
 
        /* stop anything currently running */
+       /* pacer stop source: SOFTWARE */
        writel(0, devpriv->las0 + LAS0_PACER_STOP);
-       writel(0, devpriv->las0 + LAS0_PACER);
+       writel(0, devpriv->las0 + LAS0_PACER);  /* stop pacer */
        writel(0, devpriv->las0 + LAS0_ADC_CONVERSION);
        devpriv->intMask = 0;
        writew(devpriv->intMask, devpriv->las0 + LAS0_IT);
@@ -1215,12 +1218,17 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
        /* setup the common case and override if needed */
        if (cmd->chanlist_len > 1) {
                /*DPRINTK ("rtd520: Multi channel setup\n"); */
+               /* pacer start source: SOFTWARE */
                writel(0, devpriv->las0 + LAS0_PACER_START);
+               /* burst trigger source: PACER */
                writel(1, devpriv->las0 + LAS0_BURST_START);
+               /* ADC conversion trigger source: BURST */
                writel(2, devpriv->las0 + LAS0_ADC_CONVERSION);
        } else {                /* single channel */
                /*DPRINTK ("rtd520: single channel setup\n"); */
+               /* pacer start source: SOFTWARE */
                writel(0, devpriv->las0 + LAS0_PACER_START);
+               /* ADC conversion trigger source: PACER */
                writel(1, devpriv->las0 + LAS0_ADC_CONVERSION);
        }
        writel((devpriv->fifoLen / 2 - 1) & 0xffff, devpriv->las0 + LAS0_ACNT);
@@ -1269,7 +1277,9 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
                devpriv->transCount = 0;
                devpriv->flags &= ~SEND_EOS;
        }
+       /* pacer clock source: INTERNAL 8MHz */
        writel(1, devpriv->las0 + LAS0_PACER_SELECT);
+       /* just interrupt, don't stop */
        writel(1, devpriv->las0 + LAS0_ACNT_STOP_ENABLE);
 
        /* BUG??? these look like enumerated values, but they are bit fields */
@@ -1305,6 +1315,7 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
                break;
 
        case TRIG_EXT:
+               /* pacer start source: EXTERNAL */
                writel(1, devpriv->las0 + LAS0_PACER_START);
                break;
 
@@ -1327,6 +1338,7 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
                break;
 
        case TRIG_EXT:          /* external */
+               /* burst trigger source: EXTERNAL */
                writel(2, devpriv->las0 + LAS0_BURST_START);
                break;
 
@@ -1378,7 +1390,7 @@ static int rtd_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 
        /* BUG: start_src is ASSUMED to be TRIG_NOW */
        /* BUG? it seems like things are running before the "start" */
-       readl(devpriv->las0 + LAS0_PACER);
+       readl(devpriv->las0 + LAS0_PACER);      /* start pacer */
        return 0;
 }
 
@@ -1391,8 +1403,9 @@ static int rtd_ai_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
        u32 overrun;
        u16 status;
 
+       /* pacer stop source: SOFTWARE */
        writel(0, devpriv->las0 + LAS0_PACER_STOP);
-       writel(0, devpriv->las0 + LAS0_PACER);
+       writel(0, devpriv->las0 + LAS0_PACER);  /* stop pacer */
        writel(0, devpriv->las0 + LAS0_ADC_CONVERSION);
        devpriv->intMask = 0;
        writew(devpriv->intMask, devpriv->las0 + LAS0_IT);