igb: acknowledging time sync interrupts

igb: acknowledging time sync interrupts

[Richard Cochran]

Matt,

In igb_main.c you have ISR code like:

	if (icr & E1000_ICR_TS) {
		u32 tsicr = rd32(E1000_TSICR);

		if (tsicr & E1000_TSICR_TXTS) {
			/* acknowledge the interrupt */
			wr32(E1000_TSICR, E1000_TSICR_TXTS);
			/* retrieve hardware timestamp */
			schedule_work(&adapter->ptp_tx_work);
		}
	}

In the datasheet for the 82580 and the i210, for TSICR it says,

   Note: Once ICR.Time_Sync is set, the internal value of this
         register should be cleared by writing 1b to all bits
         or cleared by a read to enable receiving an additional
         ^^^^^^^^^^^^^^^^^^^^
         ICR.Time_Sync interrupt.

and that implies that your write to acknowledge the interrupt is
superfluous, since you already read the TSICR.

Is this an error in the datasheets, or is the code doing extra,
unneeded work?

Thanks,
Richard

Re: igb: acknowledging time sync interrupts

[Vick, Matthew]

On 5/26/13 3:39 AM, "Richard Cochran" <richardcochran@gmail.com> wrote:

>Matt,
>
>In igb_main.c you have ISR code like:
>
>	if (icr & E1000_ICR_TS) {
>		u32 tsicr = rd32(E1000_TSICR);
>
>		if (tsicr & E1000_TSICR_TXTS) {
>			/* acknowledge the interrupt */
>			wr32(E1000_TSICR, E1000_TSICR_TXTS);
>			/* retrieve hardware timestamp */
>			schedule_work(&adapter->ptp_tx_work);
>		}
>	}
>
>In the datasheet for the 82580 and the i210, for TSICR it says,
>
>   Note: Once ICR.Time_Sync is set, the internal value of this
>         register should be cleared by writing 1b to all bits
>         or cleared by a read to enable receiving an additional
>         ^^^^^^^^^^^^^^^^^^^^
>         ICR.Time_Sync interrupt.
>
>and that implies that your write to acknowledge the interrupt is
>superfluous, since you already read the TSICR.
>
>Is this an error in the datasheets, or is the code doing extra,
>unneeded work?
>
>Thanks,
>Richard

Richard,

Good catch--and you're correct--but I had issues with the read of TSICR
not clearing like it should on the 82580 (but it would work fine on the
I350 and I210). I decided the cleaner implementation would be to
explicitly acknowledge the interrupt across the board. I haven't had the
time to follow up with the hardware team, but my suspicion is that it's an
errata with the 82580.

I'll start some internal discussion to see if I can get an official answer
on the 82580.

Cheers,
Matthew


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Re: igb: acknowledging time sync interrupts

[Richard Cochran]

On Tue, May 28, 2013 at 03:20:10PM +0000, Vick, Matthew wrote:
> 
> I'll start some internal discussion to see if I can get an official answer
> on the 82580.

Okay, that sounds good. I just posted a patch that removes the wr32(),
and I can report that it does work on the i210. If the 82580 needs
this workaround, then I can add it back in again.

Thanks,
Richard

Re: igb: acknowledging time sync interrupts

[Vick, Matthew]

On 5/28/13 9:06 AM, "Richard Cochran" <richardcochran@gmail.com> wrote:

>On Tue, May 28, 2013 at 03:20:10PM +0000, Vick, Matthew wrote:
>> 
>> I'll start some internal discussion to see if I can get an official
>>answer
>> on the 82580.
>
>Okay, that sounds good. I just posted a patch that removes the wr32(),
>and I can report that it does work on the i210. If the 82580 needs
>this workaround, then I can add it back in again.
>
>Thanks,
>Richard

Following up internally, we got confirmation 82580 does have an issue with
the read of TSICR not clearing it. Please do add the wr32 back in and keep
an eye out for updated documentation.

Cheers,
Matthew