Re: [PATCH net-next v7 08/10] net: dsa: realtek: rtl8365mb: re-latch the family D SerDes

[Alvin Šipraga]

On Fri, Nov 06, 2026 at 03:56:10PM +0100, Mieczyslaw Nalewaj wrote:
> Subject: Re: [PATCH net-next v7 08/10] net: dsa: realtek: rtl8365mb: re-latch the family D SerDes
> 
> On Fri, Nov 06, 2026 at 03:28:30PM +0100, Alvin Šipraga wrote:
> > I don't understand this at all, should it be obvious what you mean by
> > "edge" and "latch" here? I would assume you are talking about interrupts
> > but it's not clear.
> 
> Sorry, the wording was unclear, and no interrupts are involved. "Edge"
> is the SDS_MISC mode field changing from DISABLE to HSGMII, and "latch"
> is the SerDes receiver locking onto the incoming signal. It locks on
> that change, not on the value, and only if the far end is already
> sending.
> 
> > Is the shortcoming/issue you are addressing one of DSA when a SerDes is
> > used in the CPU link? Or is it rather some hardware oddity?
> 
> As far as I can tell, a hardware oddity. If the change happens before
> the far-end MAC is up, the receiver does not lock and nothing retries.
> Both ends then report 2.5Gbps/Full while no frames pass.
> 
> > Can we use interrupts instead of polling?
> 
> I do not know. I have no datasheet, and the vendor API I have does not
> expose an interrupt for the SerDes state.
> 
> > I'm basically wondering here if this is not something that DSA or
> > phylink could help with?
> 
> pcs_config() and pcs_link_up() run seconds before the far-end MAC
> starts, and phylink never calls rtl8365mb_pcs_get_state() for this
> port: mb->pcs.poll only arms polling for in-band links, and the CPU
> port is a fixed link. The only event I found that tells the driver the
> far end is starting is the CPU conduit coming up, reported through
> ->conduit_state_change().

OK. Unfortunately I'm a bit out of my depth here, not having worked with
SerDes links before. My gut tells me this patch is overkill. I hope
somebody else with more experience can chip in. Adding Johan to the
mail, as he added SGMII support and might have some opinters.

Kind regards,
Alvin