RE: [PATCH iwl-net] igc: Fix hicredit calculation

[Rodrigo CADORE CATALDO <rodrigo.cadore@l-acoustics.com>]

> -----Original Message-----
> From: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> 
> Rodrigo Cataldo via B4 Relay
> <devnull+rodrigo.cadore.l-acoustics.com@kernel.org> writes:
> 
> > From: Rodrigo Cataldo <rodrigo.cadore@l-acoustics.com>
> >
> > According to the Intel Software Manual for I225, Section 7.5.2.7,
> > hicredit should be multiplied by the constant link-rate value, 0x7736.
> >
> > Currently, the old constant link-rate value, 0x7735, from the boards
> > supported on igb are being used, most likely due to a copy'n'paste, as
> > the rest of the logic is the same for both drivers.
> >
> > Update hicredit accordingly.
> >
> > Fixes: 1ab011b0bf07 ("igc: Add support for CBS offloading")
> > Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
> > Signed-off-by: Rodrigo Cataldo <rodrigo.cadore@l-acoustics.com>
> > ---
> 
> Very good catch.
> 
> Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> 
> Just for curiosity, my test machines are busy right now, what kind of
> difference are you seeing?
> 

Hello Vinicius, thank you for the ACK.

For our internal setup, this does not make a difference. My understanding is 
that hicredit is used for non-SR traffic mixed with SR traffic (i.e., hicredit is
directly related to the max non-SR frame size). But our setup does not mix
them (q0 is used only for milan audio/clock SR class A).

Let me know if you think we need a testcase for this.

> > This is a simple fix for the credit calculation on igc devices
> > (i225/i226) to match the Intel software manual.
> >
> > This is my first contribution to the Linux Kernel. Apologies for any
> > mistakes and let me know if I improve anything.
> > ---
> >  drivers/net/ethernet/intel/igc/igc_tsn.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/intel/igc/igc_tsn.c
> b/drivers/net/ethernet/intel/igc/igc_tsn.c
> > index a9c08321aca9..22cefb1eeedf 100644
> > --- a/drivers/net/ethernet/intel/igc/igc_tsn.c
> > +++ b/drivers/net/ethernet/intel/igc/igc_tsn.c
> > @@ -227,7 +227,7 @@ static int igc_tsn_enable_offload(struct igc_adapter
> *adapter)
> >                       wr32(IGC_TQAVCC(i), tqavcc);
> >
> >                       wr32(IGC_TQAVHC(i),
> > -                          0x80000000 + ring->hicredit * 0x7735);
> > +                          0x80000000 + ring->hicredit * 0x7736);
> >               } else {
> >                       /* Disable any CBS for the queue */
> >                       txqctl &= ~(IGC_TXQCTL_QAV_SEL_MASK);
> >
> > ---
> > base-commit: 2078a341f5f609d55667c2dc6337f90d8f322b8f
> > change-id: 20231206-igc-fix-hicredit-calc-028bf73c50a8
> >
> > Best regards,
> > --
> > Rodrigo Cataldo <rodrigo.cadore@l-acoustics.com>
> >
> 
> Cheers,
> --
> Vinicius

Best Regards,
Rodrigo Cataldo