Re: [PATCH net-next 2/2] net: macb: configure ENST registers for all queues

[Karumanchi, Vineeth]

Hi Théo Lebrun,

On 7/24/2026 11:36 PM, Théo Lebrun wrote:
> Hello Vineeth,
>
> On Fri Jul 24, 2026 at 6:32 AM CEST, Vineeth Karumanchi wrote:
> > The initial "tc" command was not overwriting the reset value of ENST
> > registers if only a subset of queues were configured, leading to an
> > invalid setup. To fix this, configure all queues unconditionally.
> > Unconfigured queues are zero-initialized via kcalloc(), ensuring a
> > complete and consistent configuration.
> But if a subset of queues are configured, the remaining queues don't
> have their ENST support enabled thanks to ENST_CONTROL and their ENST
> per-queue register values aren't read? Or HW is broken and reads ENST
> registers anyway? Or something else I misunderstood?
>
> What reset value of ENST regs you observed that caused you trouble?
> That info could make it into the commit message.
//
Yes, this is a confirmed hardware issue. We raised it with Cadence, and 
they have
acknowledged the problem. The reset value of the |enst_on_time_qX| 
registers is *0x0001FFFF*.

During ENST initialization, packet interleaving was observed when only a
subset of the available queues was configured, while the remaining 
queues—whose
corresponding |enst_on_time_qX| registers still contained non-zero 
values—were left disabled in |ENST_CONTROL|.


For example, in a configuration where only two of the four queues are 
enabled,
some packets from *Q0* getting transmitted during the *Q1* time slot, 
and vice versa.

Furthermore, once the hardware enters this state, it does not recover 
even after a
complete ENST queue reconfiguration is performed.

Thanks

🙏 Vineeth

> > The queue_id field in struct macb_queue_enst_config becomes redundant
> > once the array is indexed by queue id, so drop it.
> >
> > Key changes:
> > - Drop queue_id from struct macb_queue_enst_config
> > - Allocate enst_queue[] based on bp->num_queues instead of
> >    conf->num_entries
> > - Index enst_queue[] directly with the queue number
> > - Program ENST registers for all queues
> >
> > Fixes: 89934dbf169e ("net: macb: Add TAPRIO traffic scheduling support")
> > Signed-off-by: Vineeth Karumanchi <vineeth.karumanchi@xxxxxxx>
> Thanks,
>
> --
> Théo Lebrun, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com