staging: comedi: das16: fix DMA init during board attach

DMA support is optional in this driver. To enable it, the user
passes the desired DMA channel during the board attach. A timer
is then used by the driver to periodically get the analog input
data from the DMA.

Since the DMA support is optional, modify the init code so that
it only fails if the DMA channel is unavailable or the DMA buffers
can not be allocated. Don't fail just because the user passed an
invalid DMA channel (only DMA channels 1 and 3 are valid).

Remove the printk() noise about the DMA. Change the printk() when
the request_dma() fails into a dev_err().

Move the timer initialization so it's only setup if DMA is available.
It's not needed otherwise. Also, only hook up the subdevice command
support functions if DMA is available. This allows removing a couple
sanity checks in the command support.
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>

drivers/staging/comedi/drivers/das16.c

@@ -633,7 +633,6 @@ static int das16_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
 	/* disable interrupts, dma and pacer clocked conversions */
 	devpriv->control_state &= ~DAS16_INTE & ~PACING_MASK & ~DMA_ENABLE;
 	outb(devpriv->control_state, dev->iobase + DAS16_CONTROL);
-	if (devpriv->dma_chan)
 	disable_dma(devpriv->dma_chan);
 
 	/*  disable SW timer */
@@ -821,11 +820,6 @@ static void das16_interrupt(struct comedi_device *dev)
 	async = s->async;
 	cmd = &async->cmd;
 
-	if (devpriv->dma_chan == 0) {
-		comedi_error(dev, "interrupt with no dma channel?");
-		return;
-	}
-
 	spin_lock_irqsave(&dev->spinlock, spin_flags);
 	if ((devpriv->control_state & DMA_ENABLE) == 0) {
 		spin_unlock_irqrestore(&dev->spinlock, spin_flags);
@@ -987,10 +981,10 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	const struct das16_board *board = comedi_board(dev);
 	struct das16_private_struct *devpriv;
 	struct comedi_subdevice *s;
+	struct comedi_krange *user_ai_range;
+	struct comedi_krange *user_ao_range;
+	unsigned int dma_chan = it->options[2];
 	int ret;
-	unsigned int dma_chan;
-	unsigned long flags;
-	struct comedi_krange *user_ai_range, *user_ao_range;
 
 	/*  check that clock setting is valid */
 	if (it->options[3]) {
@@ -1040,34 +1034,37 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	}
 
 	/* initialize dma */
-	dma_chan = it->options[2];
 	if (dma_chan == 1 || dma_chan == 3) {
-		/*  allocate dma buffers */
+		unsigned long flags;
 		int i;
-		for (i = 0; i < 2; i++) {
-			devpriv->dma_buffer[i] = pci_alloc_consistent(
-						NULL, DAS16_DMA_SIZE,
-						&devpriv->dma_buffer_addr[i]);
 
-			if (devpriv->dma_buffer[i] == NULL)
-				return -ENOMEM;
-		}
 		if (request_dma(dma_chan, dev->board_name)) {
-			printk(KERN_ERR " failed to allocate dma channel %i\n",
+			dev_err(dev->class_dev,
+				"failed to request dma channel %i\n",
 				dma_chan);
 			return -EINVAL;
 		}
 		devpriv->dma_chan = dma_chan;
+
+		/* allocate dma buffers */
+		for (i = 0; i < 2; i++) {
+			void *p;
+
+			p = pci_alloc_consistent(NULL, DAS16_DMA_SIZE,
+						 &devpriv->dma_buffer_addr[i]);
+			if (!p)
+				return -ENOMEM;
+			devpriv->dma_buffer[i] = p;
+		}
+
 		flags = claim_dma_lock();
 		disable_dma(devpriv->dma_chan);
 		set_dma_mode(devpriv->dma_chan, DMA_MODE_READ);
 		release_dma_lock(flags);
-		printk(KERN_INFO " ( dma = %u)\n", dma_chan);
-	} else if (dma_chan == 0) {
-		printk(KERN_INFO " ( no dma )\n");
-	} else {
-		printk(KERN_ERR " invalid dma channel\n");
-		return -EINVAL;
+
+		init_timer(&(devpriv->timer));
+		devpriv->timer.function = das16_timer_interrupt;
+		devpriv->timer.data = (unsigned long)dev;
 	}
 
 	/*  get any user-defined input range */
@@ -1098,20 +1095,15 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 		user_ao_range->flags = UNIT_volt;
 	}
 
-	init_timer(&(devpriv->timer));
-	devpriv->timer.function = das16_timer_interrupt;
-	devpriv->timer.data = (unsigned long)dev;
-
 	ret = comedi_alloc_subdevices(dev, 5);
 	if (ret)
 		return ret;
 
 	s = &dev->subdevices[0];
-	dev->read_subdev = s;
 	/* ai */
 	if (board->ai) {
 		s->type = COMEDI_SUBD_AI;
-		s->subdev_flags = SDF_READABLE | SDF_CMD_READ;
+		s->subdev_flags = SDF_READABLE;
 		if (devpriv->ai_singleended) {
 			s->n_chan = 16;
 			s->len_chanlist = 16;
@@ -1130,10 +1122,14 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 			s->range_table = das16_ai_bip_lranges[board->ai_pg];
 		}
 		s->insn_read = board->ai;
+		if (devpriv->dma_chan) {
+			dev->read_subdev = s;
+			s->subdev_flags |= SDF_CMD_READ;
 			s->do_cmdtest = das16_cmd_test;
 			s->do_cmd = das16_cmd_exec;
 			s->cancel = das16_cancel;
 			s->munge = das16_ai_munge;
+		}
 	} else {
 		s->type = COMEDI_SUBD_UNUSED;
 	}