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

[Birger Koblitz <mail@birger-koblitz.de>]

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@birger-koblitz.de>
>> ---
>>   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