[PATCH] 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, use a static dummy fallback device structure
with the coherent DMA mask set to the ISA bus limit of 16MB.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
 drivers/staging/comedi/drivers/comedi_isadma.c | 15 +++++++++++++--
 drivers/staging/comedi/drivers/comedi_isadma.h |  3 +++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/drivers/comedi_isadma.c b/drivers/staging/comedi/drivers/comedi_isadma.c
index b77dc8d5d3ff..8929952516a1 100644
--- a/drivers/staging/comedi/drivers/comedi_isadma.c
+++ b/drivers/staging/comedi/drivers/comedi_isadma.c
@@ -14,6 +14,16 @@
 
 #include "comedi_isadma.h"
 
+/*
+ * Fallback device used when hardware device is NULL.
+ * This can be removed after drivers have been converted to use isa_driver.
+ */
+static struct device fallback_dev = {
+	.init_name = "comedi_isadma fallback device",
+	.coherent_dma_mask = DMA_BIT_MASK(24),
+	.dma_mask = &fallback_dev.coherent_dma_mask,
+};
+
 /**
  * comedi_isadma_program - program and enable an ISA DMA transfer
  * @desc:	the ISA DMA cookie to program and enable
@@ -172,6 +182,7 @@ struct comedi_isadma *comedi_isadma_alloc(struct comedi_device *dev,
 		goto no_dma;
 	dma->desc = desc;
 	dma->n_desc = n_desc;
+	dma->dev = dev->hw_dev ? dev->hw_dev : &fallback_dev;
 
 	dma_chans[0] = dma_chan1;
 	if (dma_chan2 == 0 || dma_chan2 == dma_chan1)
@@ -192,7 +203,7 @@ 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 +235,7 @@ 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