[PATCH v2] staging: comedi: comedi_isadma: Use a non-NULL device for DMA API

[Ian Abbott]

The "comedi_isadma" module calls `dma_alloc_coherent()` and
`dma_free_coherent()` with a NULL device pointer which is no longer
allowed.  If the `hw_dev` member of the `struct comedi_device` has been
set to a valid device, that can be used instead.  Unfortunately, all the
current users of the "comedi_isadma" module leave the `hw_dev` member
set to NULL.  In that case, fall back to using the comedi "class" device
pointed to by the `class_dev` member if that is non-NULL.  In that case,
make it "DMA-capable" with a coherent DMA mask set to the ISA bus limit
of 16MB (24 bits).

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
v2: Use the comedi "class" device instead of a static fallback device.
---
 drivers/staging/comedi/drivers/comedi_isadma.c | 17 +++++++++++++++--
 drivers/staging/comedi/drivers/comedi_isadma.h |  3 +++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/drivers/comedi_isadma.c b/drivers/staging/comedi/drivers/comedi_isadma.c
index b77dc8d5d3ff..c729094298c2 100644
--- a/drivers/staging/comedi/drivers/comedi_isadma.c
+++ b/drivers/staging/comedi/drivers/comedi_isadma.c
@@ -172,6 +172,19 @@ struct comedi_isadma *comedi_isadma_alloc(struct comedi_device *dev,
 		goto no_dma;
 	dma->desc = desc;
 	dma->n_desc = n_desc;
+	if (dev->hw_dev) {
+		dma->dev = dev->hw_dev;
+	} else {
+		/* Fall back to using the "class" device. */
+		if (!dev->class_dev)
+			goto no_dma;
+		/* Need 24-bit mask for ISA DMA. */
+		if (dma_coerce_mask_and_coherent(dev->class_dev,
+						 DMA_BIT_MASK(24))) {
+			goto no_dma;
+		}
+		dma->dev = dev->class_dev;
+	}
 
 	dma_chans[0] = dma_chan1;
 	if (dma_chan2 == 0 || dma_chan2 == dma_chan1)
@@ -192,7 +205,7 @@ struct comedi_isadma *comedi_isadma_alloc(struct comedi_device *dev,
 		desc = &dma->desc[i];
 		desc->chan = dma_chans[i];
 		desc->maxsize = maxsize;
-		desc->virt_addr = dma_alloc_coherent(NULL, desc->maxsize,
+		desc->virt_addr = dma_alloc_coherent(dma->dev, desc->maxsize,
 						     &desc->hw_addr,
 						     GFP_KERNEL);
 		if (!desc->virt_addr)
@@ -224,7 +237,7 @@ void comedi_isadma_free(struct comedi_isadma *dma)
 		for (i = 0; i < dma->n_desc; i++) {
 			desc = &dma->desc[i];
 			if (desc->virt_addr)
-				dma_free_coherent(NULL, desc->maxsize,
+				dma_free_coherent(dma->dev, desc->maxsize,
 						  desc->virt_addr,
 						  desc->hw_addr);
 		}
diff --git a/drivers/staging/comedi/drivers/comedi_isadma.h b/drivers/staging/comedi/drivers/comedi_isadma.h
index 2bd1329d727f..9d2b12db7e6e 100644
--- a/drivers/staging/comedi/drivers/comedi_isadma.h
+++ b/drivers/staging/comedi/drivers/comedi_isadma.h
@@ -10,6 +10,7 @@
 #include <linux/types.h>
 
 struct comedi_device;
+struct device;
 
 /*
  * These are used to avoid issues when <asm/dma.h> and the DMA_MODE_
@@ -38,6 +39,7 @@ struct comedi_isadma_desc {
 
 /**
  * struct comedi_isadma - ISA DMA data
+ * @dev:	device to allocate non-coherent memory for
  * @desc:	cookie for each DMA buffer
  * @n_desc:	the number of cookies
  * @cur_dma:	the current cookie in use
@@ -45,6 +47,7 @@ struct comedi_isadma_desc {
  * @chan2:	the second DMA channel requested
  */
 struct comedi_isadma {
+	struct device *dev;
 	struct comedi_isadma_desc *desc;
 	int n_desc;
 	int cur_dma;
-- 
2.20.1