On Wed, Sep 12, 2018 at 10:00:57AM -0700, Nick Desaulniers wrote:

On Tue, Sep 11, 2018 at 4:40 PM Nathan Chancellor
[off-list ref] wrote:

quoted

Clang warns when implicitly converting from one enumerated type to
another. Avoid this by using the equivalent value from the expected
type.

In file included from drivers/dma/ep93xx_dma.c:30:
./include/linux/platform_data/dma-ep93xx.h:88:10: warning: implicit
conversion from enumeration type 'enum dma_data_direction' to different
enumeration type 'enum dma_transfer_direction' [-Wenum-conversion]
                return DMA_NONE;
                ~~~~~~ ^~~~~~~~
1 warning generated.

Reported-by: Nick Desaulniers <redacted>
Signed-off-by: Nathan Chancellor <redacted>
---
 include/linux/platform_data/dma-ep93xx.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/platform_data/dma-ep93xx.h b/include/linux/platform_data/dma-ep93xx.h
index f8f1f6b952a6..eb9805bb3fe8 100644
--- a/include/linux/platform_data/dma-ep93xx.h
+++ b/include/linux/platform_data/dma-ep93xx.h

@@ -85,7 +85,7 @@ static inline enum dma_transfer_direction
 ep93xx_dma_chan_direction(struct dma_chan *chan)
 {
        if (!ep93xx_dma_chan_is_m2p(chan))
-               return DMA_NONE;
+               return DMA_TRANS_NONE;

Looks like this changes the value of the returned enum from:
DMA_NONE: 3
DMA_TRANS_NONE: 4

Hopefully the DMA maintainer can review if this was ever correct?
Looks like the callers of ep93xx_dma_chan_direction were comparing
this return type, so those comparisons would likely always be failing
if `!ep93xx_dma_chan_is_m2p(chan)`.

Normally this warning (-Wenum-conversion) is kind of noisey, but it's
concerning when the enumerated values evaluate to different integers.
I think it's found an actual bug here.
Reviewed-by: Nick Desaulniers <redacted>

I should have highlighted this in the actual commit message but I
checked all of the callsites of ep93xx_dma_chan_direction and one
directly refers to an enum value, DMA_MEM_TO_DEV; every other one
just checks if the value is or isn't equal to another value of this
enum type (DMA_NONE isn't referenced anywhere else in this driver).
I don't believe this results in a funcitonal change.

Thanks for the review!
Nathan

quoted

        /* even channels are for TX, odd for RX */
        return (chan->chan_id % 2 == 0) ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
--
2.18.0

-- 
Thanks,
~Nick Desaulniers