Re: [PATCH v2] net: stmmac: enable MAC rx/tx after DMA start

[Jakub Kicinski]

On Mon, 27 Jul 2026 10:23:13 +0200 Maxime Chevallier wrote:
> On 7/27/26 08:14, Abid Ali wrote:
> > When the MAC receiver is enabled before the DMA channels are started,
> > incoming frames fill the MTL FIFO with no DMA engine to drain it.
> > If the PHY/Switch is already up at this point, and there is inflow
> > of packets towards EMAC, the per-queue FIFO overflows within this window.
> > 
> > Once the FIFO is full, the MTL read controller goes idle and never
> > retries delivery even if the DMA comes alive later on.
> > This behaviour happens due to enabling the MAC RX path before
> > the DMA setup is ready, and any delay between these events increases
> > the chances of blocking the rx path permanently.
> > 
> > The EMAC should only accept packets after the DMAs are enabled.
> > Similarly, the teardown should ensure the MAC rx/tx is stopped before
> > DMA engine is stopped.
> > 
> > Signed-off-by: Abid Ali <dev.taqnialabs@xxxxxxxxx>  
> 
> Ah great ! This matches the programming model for the few ref manuals I
> have, e.g. cycloneV manual does state that the MAC must be enabled after the
> DMA has been configured.

Sorry, me+Sashiko again :S

Sashiko wrote a damn essay, IDK if it makes sense.

Looking at the patch - isn't it a bit awkward to handle Rx and Tx
together? We want to keep Rx blocked to prevent incoming frames,
but Tx should be allowed so that Tx can egress?

Grepping around I'm not seeing any flushing of Tx. Aren't there
issues with this driver if we stop the interface while it was
paused by link partner?
-- 
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