[v2] net: altera_tse: fix msgdma_tx_completion on non-zero fill_level case

From: Tomonori Sakita <tomonori.sakita@sord.co.jp>

If fill_level was not zero and status was not BUSY,
result of "tx_prod - tx_cons - inuse" might be zero.
Subtracting 1 unconditionally results invalid negative return value
on this case.
Make sure not to return an negative value.

Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
Reviewed-by: Dalon L Westergreen <dalon.westergreen@linux.intel.com>
---
Changes in v2:
  Use max_t instead of just removing the "- 1".

 drivers/net/ethernet/altera/altera_msgdma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On 1/24/19 8:02 PM, Atsushi Nemoto wrote:
> From: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> 
> If fill_level was not zero and status was not BUSY,
> result of "tx_prod - tx_cons - inuse" might be zero.
> Subtracting 1 unconditionally results invalid negative return value
> on this case.
> Make sure not to return an negative value.
> 
> Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> Reviewed-by: Dalon L Westergreen <dalon.westergreen@linux.intel.com>
> ---
> Changes in v2:
>    Use max_t instead of just removing the "- 1".
> 
>   drivers/net/ethernet/altera/altera_msgdma.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/altera/altera_msgdma.c b/drivers/net/ethernet/altera/altera_msgdma.c
> index 0fb986b..0ae723f 100644
> --- a/drivers/net/ethernet/altera/altera_msgdma.c
> +++ b/drivers/net/ethernet/altera/altera_msgdma.c
> @@ -145,7 +145,8 @@ u32 msgdma_tx_completions(struct altera_tse_private *priv)
>   			& 0xffff;
>   
>   	if (inuse) { /* Tx FIFO is not empty */
> -		ready = priv->tx_prod - priv->tx_cons - inuse - 1;
> +		ready = max_t(int,
> +			      priv->tx_prod - priv->tx_cons - inuse - 1, 0);
>   	} else {
>   		/* Check for buffered last packet */
>   		status = csrrd32(priv->tx_dma_csr, msgdma_csroffs(status));
> 

Thanks for the patch!

Acked-by: Thor Thayer <thor.thayer@linux.intel.com>

From: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
Date: Fri, 25 Jan 2019 11:02:22 +0900

> From: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> 
> If fill_level was not zero and status was not BUSY,
> result of "tx_prod - tx_cons - inuse" might be zero.
> Subtracting 1 unconditionally results invalid negative return value
> on this case.
> Make sure not to return an negative value.
> 
> Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> Reviewed-by: Dalon L Westergreen <dalon.westergreen@linux.intel.com>
> ---
> Changes in v2:
>   Use max_t instead of just removing the "- 1".

Applied.