Re: [PATCH] dmaengine: virt-dma: fix completion list manipulation
From: Robert Jarzmik
Date: Mon Mar 02 2015 - 17:03:41 EST
Lars-Peter Clausen <lars@xxxxxxxxxx> writes:
> On 03/02/2015 10:19 PM, Robert Jarzmik wrote:
>> diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
>> index 3772032..2a3da22 100644
>> --- a/drivers/dma/virt-dma.h
>> +++ b/drivers/dma/virt-dma.h
>> @@ -91,7 +91,7 @@ static inline void vchan_cookie_complete(struct virt_dma_desc *vd)
>> dma_cookie_complete(&vd->tx);
>> dev_vdbg(vc->chan.device->dev, "txd %p[%x]: marked complete\n",
>> vd, cookie);
>> - list_add_tail(&vd->node, &vc->desc_completed);
>> + list_move_tail(&vd->node, &vc->desc_completed);
>
> That will break all drivers which handle this currently correctly and remove the
> descriptor from any list before calling vchan_cookie_complete.
Ah, well well I don't agree.
First, let's split the drivers which remove the descriptors and these which
don't :
These which remove the descriptor:
dma-jz4740.c
fsl-edma.c
These which don't remove the descriptor:
amba-pl08x.c
edma.c
img-mdc-dma.c
k3dma.c
moxart-dma.c
omap-dma.c
qcom_bam_dma.c
s3c24xx-dma.c
sa11x0-dma.c
sun6i-dma.c
That settles the correctness I think, the correct behavior is to not remove the
descriptor and let it be done by vchan_cookie_complete().
Now for the remaining 2 drivers, we'll have :
- list_del(&vd->node) => vd becomes a singleton
- list_move_tail(&vd->node, &...desc_completed)
=> list_del(&vd->node) : nothing changes, it's a nop
=> list_add_tail(&vd->node, &...desc_completed)
And the behavior remains correct after the patch, only one "list_del()" is done
twice for nothing. Where do you see any breakage ?
Cheers.
--
Robert
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