Re: [PATCH v5 4/4] DMA: Freescale: eliminate a compiling warning

[Hongbo Zhang]

On 07/25/2013 03:33 AM, Scott Wood wrote:
> On 07/24/2013 01:21:09 AM, hongbo.zhang@xxxxxxxxxxxxx wrote:
> > From: Hongbo Zhang <hongbo.zhang@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxx>
> > ---
> >  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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