RE: [PATCH] powerpc : dma-mapping : Check null condition for dev->archdata.dma_ops

-----Original Message-----
From: Denis Kirjanov [mailto:kirjanov@gmail.com]
Sent: Friday, July 18, 2014 7:21 PM
To: Badola Nikhil-B46172
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc : dma-mapping : Check null condition for dev=

-

quoted

archdata.dma_ops

=20
On 7/18/14, Nikhil Badola [off-list ref] wrote:

quoted

Modifies get_dma_ops() implementation on ppc arch to check null
condition

 which means that dma is not supported.
=20
Could you please describe the use case where the ops is null.

The use case in which ops are null is while running USB in Gadget and Otg m=
ode.

For PPC architecture, whenever a platform device is registered, pdev->dev i=
s=20
assigned dma_ops.=20
In USB, one single chipidea platform device is registered for any mode (hos=
t, gadget or otg)
whose dev, as explained above, has dma_ops set and this dev is assigned to =
 ci->dev(dev of chipidea struct)
which is used by host controller device. That is why we don't need the abov=
e null case checking in
host mode. But when we run usb in gadget/otg mode, the device structure use=
d is ci->gadget.dev
which does not have dma_ops set and it crashes when dma transaction starts =
when it calls get_dma_ops()
which returns NULL.

A similar approach is used in ARM architecture which checks for null condit=
ion and returns=20
common dma_ops

=20

quoted

for dev->archdata.dma_ops; returns common dma_direct_ops structure in
case its NULL

Signed-off-by: Nikhil Badola <redacted>
---
 arch/powerpc/include/asm/dma-mapping.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/dma-mapping.h

b/arch/powerpc/include/asm/dma-mapping.h
index 150866b..d73bae8 100644

--- a/arch/powerpc/include/asm/dma-mapping.h
+++ b/arch/powerpc/include/asm/dma-mapping.h

@@ -86,10 +86,12 @@ static inline struct dma_map_ops

*get_dma_ops(struct device *dev)
 	 */
 	if (unlikely(dev =3D=3D NULL))
 		return NULL;
-
-	return dev->archdata.dma_ops;
+	if (dev->archdata.dma_ops)
+		return dev->archdata.dma_ops;
+	return &dma_direct_ops;
 }

+
 static inline void set_dma_ops(struct device *dev, struct dma_map_ops
*ops)  {
 	dev->archdata.dma_ops =3D ops;
--
1.7.11.7

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=20
=20
--
Regards,
Denis

Regards,
Nikhil