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SubjectRe: [PATCH v5 4/4] DMA: Freescale: eliminate a compiling warning
On 07/25/2013 03:33 AM, Scott Wood wrote:
> On 07/24/2013 01:21:09 AM, hongbo.zhang@freescale.com wrote:
>> From: Hongbo Zhang <hongbo.zhang@freescale.com>
>>
>> The variable cookie is initialized in a list_for_each_entry loop,
>> if(unlikely)
>> the list is empty, this variable will be used uninitialized, so we
>> get a gcc
>> compiling warning about this. This patch fixes this defect by setting an
>> initial value to the varialble cookie.
>>
>> Signed-off-by: Hongbo Zhang <hongbo.zhang@freescale.com>
>> ---
>> drivers/dma/fsldma.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
>> index 16a9a48..14d68a4 100644
>> --- a/drivers/dma/fsldma.c
>> +++ b/drivers/dma/fsldma.c
>> @@ -406,7 +406,7 @@ static dma_cookie_t fsl_dma_tx_submit(struct
>> dma_async_tx_descriptor *tx)
>> struct fsl_desc_sw *desc = tx_to_fsl_desc(tx);
>> struct fsl_desc_sw *child;
>> unsigned long flags;
>> - dma_cookie_t cookie;
>> + dma_cookie_t cookie = 0;
>>
>> spin_lock_irqsave(&chan->desc_lock, flags);
>
> This patch is unrelated to the rest of the patch series...
>
> What are the semantics of this function if there are multiple entries
> in the list? Returning the last cookie seems a bit odd.
>
> Is zero the proper error value? include/linux/dmaengine.h suggests
> that cookies should be < 0 to indicate error.
I found this compiling warning since the beginning of this work, it is
better somebody fixes it sooner or later, so I take it at last.
Yes it was a bit hard to define the initial value, I saw the
dmaengine.h, and I searched all the other DMA drivers with initial value
before making the decision:
drivers/dma/mv_xor.c: dma_cookie_t cookie = 0;
drivers/dma/sh/shdma-base.c: dma_cookie_t cookie = 0;
drivers/dma/mmp_pdma.c: dma_cookie_t cookie = -EBUSY;
drivers/dma/ppc4xx/adma.c: dma_cookie_t cookie = 0;
drivers/dma/iop-adma.c: dma_cookie_t cookie = 0;
most of them using 0, and only one negative value, it seems better? but
-EBUSY isn't so accurate I think.
My thought is to drop this in the next iteration, and back to this after
the first 3 get merged.
>
> -Scott





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