Re: [PATCH] fix dma_unmap_sg misuse

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Tuesday 17 February 2009, FUJITA Tomonori wrote:
> Looks like that libata misuses dma_unmap_sg though I'm not familiar
> with libata so I might completely misunderstand something.
> 
> =
> From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> Subject: [PATCH] fix dma_unmap_sg misuse
> 
> DMA-mapping.txt says:
> 
> To unmap a scatterlist, just call:
> 
> 	pci_unmap_sg(pdev, sglist, nents, direction);
> 
> Again, make sure DMA activity has already finished.
> 
> PLEASE NOTE:  The 'nents' argument to the pci_unmap_sg call must be
>               the _same_ one you passed into the pci_map_sg call,
> 	      it should _NOT_ be the 'count' value _returned_ from the
>               pci_map_sg call.

This is correct and other subsystems (SCSI, IDE) are compliant with it.

> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

Acked-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

> ---
>  drivers/ata/libata-core.c |    4 ++--
>  include/linux/libata.h    |    1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 9fbf059..5e324ce 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -4612,7 +4612,7 @@ void ata_sg_clean(struct ata_queued_cmd *qc)
>  	VPRINTK("unmapping %u sg elements\n", qc->n_elem);
>  
>  	if (qc->n_elem)
> -		dma_unmap_sg(ap->dev, sg, qc->n_elem, dir);
> +		dma_unmap_sg(ap->dev, sg, qc->orig_n_elem, dir);
>  
>  	qc->flags &= ~ATA_QCFLAG_DMAMAP;
>  	qc->sg = NULL;
> @@ -4727,7 +4727,7 @@ static int ata_sg_setup(struct ata_queued_cmd *qc)
>  		return -1;
>  
>  	DPRINTK("%d sg elements mapped\n", n_elem);
> -
> +	qc->orig_n_elem = qc->n_elem;
>  	qc->n_elem = n_elem;
>  	qc->flags |= ATA_QCFLAG_DMAMAP;
>  
> diff --git a/include/linux/libata.h b/include/linux/libata.h
> index 5577ea8..2de827d 100644
> --- a/include/linux/libata.h
> +++ b/include/linux/libata.h
> @@ -530,6 +530,7 @@ struct ata_queued_cmd {
>  	unsigned long		flags;		/* ATA_QCFLAG_xxx */
>  	unsigned int		tag;
>  	unsigned int		n_elem;
> +	unsigned int		orig_n_elem;
>  
>  	int			dma_dir;