> On 07/27/2021 10:55 AM Ulrich Hecht <uli@xxxxxxxx> wrote:
>
>
> > On 07/27/2021 10:21 AM Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> >
> >
> > The descriptor counters ({cur,dirty}_[rt]x) acts as free counters
> > so that conditions are possible to be incorrect when a left value
> > was overflowed.
> >
> > So, for example, ravb_tx_free() could not free any descriptors
> > because the following condition was checked as a signed value,
> > and then "NETDEV WATCHDOG" happened:
> >
> > for (; priv->cur_tx[q] - priv->dirty_tx[q] > 0; priv->dirty_tx[q]++) {
> >
> > To fix the issue, add get_num_desc() to calculate numbers of
> > remaining descriptors.
> >
> > Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> > ---
> > drivers/net/ethernet/renesas/ravb_main.c | 22 +++++++++++++++-------
> > 1 file changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> > index 805397088850..70fbac572036 100644
> > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > @@ -172,6 +172,14 @@ static const struct mdiobb_ops bb_ops = {
> > .get_mdio_data = ravb_get_mdio_data,
> > };
> >
> > +static u32 get_num_desc(u32 from, u32 subtract)
> > +{
> > + if (from >= subtract)
> > + return from - subtract;
> > +
> > + return U32_MAX - subtract + 1 + from;
> > +}
>
> This is a very roundabout way to implement an unsigned subtraction. :)
> I think it would make more sense to simply return 0 if "subtract" is larger than "from".
> (Likewise for sh_eth).
...and the tests for "> 0" should be rewritten as "!= 0". Sorry, not fully awake yet.
CU
Uli
