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

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

[Atsushi Nemoto]

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.
The subtraction is not needed if fill_level was not zero.

Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
---
 drivers/net/ethernet/altera/altera_msgdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/altera/altera_msgdma.c b/drivers/net/ethernet/altera/altera_msgdma.c
index 0fb986b..3df73d3 100644
--- a/drivers/net/ethernet/altera/altera_msgdma.c
+++ b/drivers/net/ethernet/altera/altera_msgdma.c
@@ -145,7 +145,7 @@ 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 = priv->tx_prod - priv->tx_cons - inuse;
 	} else {
 		/* Check for buffered last packet */
 		status = csrrd32(priv->tx_dma_csr, msgdma_csroffs(status));
-- 
2.1.4

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

[Thor Thayer]

On 1/21/19 2:29 AM, 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.
> The subtraction is not needed if fill_level was not zero.
> 
> Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> ---
>   drivers/net/ethernet/altera/altera_msgdma.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/altera/altera_msgdma.c b/drivers/net/ethernet/altera/altera_msgdma.c
> index 0fb986b..3df73d3 100644
> --- a/drivers/net/ethernet/altera/altera_msgdma.c
> +++ b/drivers/net/ethernet/altera/altera_msgdma.c
> @@ -145,7 +145,7 @@ 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 = priv->tx_prod - priv->tx_cons - inuse;
>   	} else {
>   		/* Check for buffered last packet */
>   		status = csrrd32(priv->tx_dma_csr, msgdma_csroffs(status));
> 

I'm adding Dalon who has done a lot of work on msgdma. I'd like to get 
his comments.

Thanks,

Thor

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

[Dalon L Westergreen]

On Tue, 2019-01-22 at 11:20 -0600, Thor Thayer wrote:
> On 1/21/19 2:29 AM, 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.
> > The subtraction is not needed if fill_level was not zero.
> > 
> > Signed-off-by: Tomonori Sakita <tomonori.sakita@sord.co.jp>
> > Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> > ---
> >   drivers/net/ethernet/altera/altera_msgdma.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/altera/altera_msgdma.c
> > b/drivers/net/ethernet/altera/altera_msgdma.c
> > index 0fb986b..3df73d3 100644
> > --- a/drivers/net/ethernet/altera/altera_msgdma.c
> > +++ b/drivers/net/ethernet/altera/altera_msgdma.c
> > @@ -145,7 +145,7 @@ 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 = priv->tx_prod - priv->tx_cons - inuse;
dont think my last email went through..

I am not sure about this.  This register indicates the number of entries
still to be processed by the dma.  the -1 is intended to represent the
decriptor currently being processed.  If ready is 
priv->tx_prod - priv->tx_cons - inuse couldn't you end up processing 1
too many packets?  IE: ready is 1 greater then the actual completed
packets?

I do agree that we should not be returning a negative value, but i dont
think i agree removing the -1 is the answer.  perhaps just check that ready
is greater than 0?

--dalon

> >   	} else {
> >   		/* Check for buffered last packet */
> >   		status = csrrd32(priv->tx_dma_csr, msgdma_csroffs(status));
> > 
> 
> I'm adding Dalon who has done a lot of work on msgdma. I'd like to get 
> his comments.
> 
> Thanks,
> 
> Thor
> 

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

[Atsushi Nemoto]

On Wed, 23 Jan 2019 14:47:06 -0800, Dalon L Westergreen <dalon.westergreen@linux.intel.com> wrote:
>> >   	if (inuse) { /* Tx FIFO is not empty */
>> > -		ready = priv->tx_prod - priv->tx_cons - inuse - 1;
>> > +		ready = priv->tx_prod - priv->tx_cons - inuse;
> dont think my last email went through..
> 
> I am not sure about this.  This register indicates the number of entries
> still to be processed by the dma.  the -1 is intended to represent the
> decriptor currently being processed.  If ready is 
> priv->tx_prod - priv->tx_cons - inuse couldn't you end up processing 1
> too many packets?  IE: ready is 1 greater then the actual completed
> packets?
> 
> I do agree that we should not be returning a negative value, but i dont
> think i agree removing the -1 is the answer.  perhaps just check that ready
> is greater than 0?

Thank you for review.

I agree with you.  It would be OK returning a possibly off-by-one
value unless it is not an negative value.

Then, how about this instead?

--- 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));
-- 

If it was OK, I will post an updated patch.

---
Atsushi Nemoto

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

[Dalon L Westergreen]

On Thu, 2019-01-24 at 14:05 +0900, Atsushi Nemoto wrote:
> On Wed, 23 Jan 2019 14:47:06 -0800, Dalon L Westergreen <
> dalon.westergreen@linux.intel.com> wrote:
> > > >   	if (inuse) { /* Tx FIFO is not empty */
> > > > -		ready = priv->tx_prod - priv->tx_cons - inuse - 1;
> > > > +		ready = priv->tx_prod - priv->tx_cons - inuse;
> > dont think my last email went through..
> > 
> > I am not sure about this.  This register indicates the number of entries
> > still to be processed by the dma.  the -1 is intended to represent the
> > decriptor currently being processed.  If ready is 
> > priv->tx_prod - priv->tx_cons - inuse couldn't you end up processing 1
> > too many packets?  IE: ready is 1 greater then the actual completed
> > packets?
> > 
> > I do agree that we should not be returning a negative value, but i dont
> > think i agree removing the -1 is the answer.  perhaps just check that ready
> > is greater than 0?
> 
> Thank you for review.
> 
> I agree with you.  It would be OK returning a possibly off-by-one
> value unless it is not an negative value.
> 
> Then, how about this instead?
> 

This works for me. thanks.

> --- 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));