Re: [PATCH net-next 3/4] r8152: Add irq mitigation for RTL8157/9

[Birger Koblitz]

On 29/04/2026 3:56 am, Andrew Lunn wrote:
> On Tue, Apr 28, 2026 at 05:47:23AM +0200, Birger Koblitz wrote:
> > Add interrupt mitigation code for both RTL8157 and RTL8159 that prevents
> > USB interrupt callbacks with urb->status ESHUTDOWN being triggered. While the
> > issue is rarely seen on the RTL8157, without the mitigation, it is
> > common on the RTL8159:
> > [273.561863] r8152 7-1:1.0 enx88c9b3b5xxxx: Stop submitting intr, status -108
> >
> > Signed-off-by: Birger Koblitz <mail@xxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/net/usb/r8152.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> > index 8255261d73148a7b4dabe0188faf07cb1f356437..08cc3c1dae0facb2400890ba4d093c97ed56d40b 100644
> > --- a/drivers/net/usb/r8152.c
> > +++ b/drivers/net/usb/r8152.c
> > @@ -8444,6 +8444,12 @@ static void r8156_init(struct r8152 *tp)
> >   	else
> >   		r8153_u2p3en(tp, false);
> >   
> > +	if (tp->version >= RTL_VER_16) {
> > +		/* Disable Interrupt Mitigation */
> > +		ocp_byte_clr_bits(tp, MCU_TYPE_USB, 0xcf04,
> > +				  BIT(0) | BIT(1) | BIT(2) | BIT(7));
> > +	}
>
> What does interrupt mitigation do?
>
> Is this a different name for interrupt coalescence, where the MAC
> delays interrupts for a period of time so more packets are in the
> receive ring when it does interrupt, so reducing the number of
> interrupts, and bigger bursts of packets are processed at once?

I do not understand what the mechanism behind this is, there is no more
documentation in the original driver. I experimented with this for some
time and the effect that I see is that it prevents interrupts after
shutdown. That is, why it is already done in rtl8153_unload(), again 
like in the original driver, where it was more critical to prevent the 
warnings.
I was hoping that Realtek could enlighten us.

Birger