Re: [Intel-wired-lan] [PATCH iwl-net v4 4/4] igc: Work around HW bug causing missing timestamps

["naamax.meir" <naamax.meir@linux.intel.com>]

On 6/8/2023 00:32, Vinicius Costa Gomes wrote:
> There's an hardware issue that can cause missing timestamps. The bug
> is that the interrupt is only cleared if the IGC_TXSTMPH_0 register is
> read.
> 
> The bug can cause a race condition if a timestamp is captured at the
> wrong time, and we will miss that timestamp. To reduce the time window
> that the problem is able to happen, in case no timestamp was ready, we
> read the "previous" value of the timestamp registers, and we compare
> with the "current" one, if it didn't change we can be reasonably sure
> that no timestamp was captured. If they are different, we use the new
> value as the captured timestamp.
> 
> The HW bug is not easy to reproduce, got to reproduce it when smashing
> the NIC with timestamping requests from multiple applications (e.g.
> multiple ntpperf instances + ptp4l), after 10s of minutes.
> 
> This workaround has more impact when multiple timestamp registers are
> used, and the IGC_TXSTMPH_0 register always need to be read, so the
> interrupt is cleared.
> 
> Fixes: 2c344ae24501 ("igc: Add support for TX timestamping")
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> ---
>   drivers/net/ethernet/intel/igc/igc_ptp.c | 48 ++++++++++++++++++------
>   1 file changed, 37 insertions(+), 11 deletions(-)

Tested-by: Naama Meir <naamax.meir@linux.intel.com>
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