Re: [RFC PATCH 2/4] b44: Fix off-by-one error in acceptable address range

[Michael Chan <michael.chan@broadcom.com>]

On Sun, Dec 8, 2019 at 12:36 AM George Spelvin <lkml@sdf.org> wrote:
>
> The requirement is dma_addr + size <= 0x40000000, not 0x3fffffff.
>
> In a logically separate but overlapping change, this patch also
> rearranges the logic for detecting failures to use a goto rather
> than testing dma_mapping_error() twice.  The latter is expensive if
> CONFIG_DMA_API_DEBUG is set, but also for bug-proofing reasons I try to
> avoid having the same condition in two places that must be kept in sync.
>
> Signed-off-by: George Spelvin <lkml@sdf.org>
> ---
>  drivers/net/ethernet/broadcom/b44.c | 42 ++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
> index 394671230c1c..e540d5646aef 100644
> --- a/drivers/net/ethernet/broadcom/b44.c
> +++ b/drivers/net/ethernet/broadcom/b44.c
> @@ -680,12 +680,13 @@ static int b44_alloc_rx_skb(struct b44 *bp, int src_idx, u32 dest_idx_unmasked)
>
>         /* Hardware bug work-around, the chip is unable to do PCI DMA
>            to/from anything above 1GB :-( */
> -       if (dma_mapping_error(bp->sdev->dma_dev, mapping) ||
> -               mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)) {
> +       if (dma_mapping_error(bp->sdev->dma_dev, mapping))
> +               goto workaround;
> +       if (mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)+1) {

The patchset looks ok to me.  The only minor suggestion is to define
this (DMA_BIT_MASK(30) + 1) as B44_DMA_ADDR_LIMIT or something like
that so you don't have to repeat it so many times.

Thanks.