Re: [net-next,v3] net: dsa: mv88e6xxx: Add partial support for TCAM entries

[Simon Horman <horms@kernel.org>]

On Wed, Feb 25, 2026 at 01:06:26PM +0000, Cedric Jehasse wrote:
> Hi,
> 
> >> diff --git a/drivers/net/dsa/mv88e6xxx/tcam.c b/drivers/net/dsa/mv88e6xxx/tcam.c
> >> new file mode 100644
> >> index 000000000000..ed02c8798200
> >> --- /dev/null
> >> +++ b/drivers/net/dsa/mv88e6xxx/tcam.c
> >
> >[ ... ]
> >
> >> +/* insert tcam entry in ordered list and move existing entries if necessary */
> >> +static int mv88e6xxx_tcam_insert_entry(struct mv88e6xxx_chip *chip,
> >> +                                    struct mv88e6xxx_tcam_entry *entry)
> >> +{
> >> +     struct mv88e6xxx_tcam_entry *elem;
> >> +     struct list_head *hpos;
> >> +     int err;
> >> +
> >> +     list_for_each_prev(hpos, &chip->tcam.entries) {
> >> +             u8 move_idx;
> >> +
> >> +             elem = list_entry(hpos, struct mv88e6xxx_tcam_entry, list);
> >> +             if (entry->prio >= elem->prio)
> >> +                     break;
> >> +
> >> +             move_idx = elem->hw_idx + 1;
> >> +
> >> +             err = mv88e6xxx_tcam_flush_entry(chip, move_idx);
> >> +             if (err)
> >> +                     return err;
> >> +
> >> +             err = chip->info->ops->tcam_ops->entry_add(chip, elem,
> >> +                                                        move_idx);
> >> +             if (err)
> >> +                     return err;
> >> +
> >> +             elem->hw_idx = move_idx;
> >> +     }
> >
> >If entry_add() fails after some entries have already been moved to new
> >hardware positions (with their hw_idx updated), doesn't the function
> >return without rolling back those partial moves? The software list would
> >then have some entries pointing to their new positions while the gap for
> >the new entry is only partially created, leaving the TCAM in an
> >inconsistent state for subsequent operations.
> 
> I don't think this is an issue. For entries that are successfully moved the
> hw_idx points to the new index. And for entries that haven't successfully
> moved it's still pointing to the old index. Hence the hw_idx field for every
> list entry should still point to the correct TCAM index. There will be a gap
> in the TCAM entries in the hardware, but that's not an issue.
> If moving an existing entry returns an error. The rollback moving of entries
> is as likely to return an error, and potentially leave the TCAM in an
> inconsistent state.

Thanks, for the clarification.
That makes sense to me.