Re: [PATCH] net: fec: don't reset irq coalesce settings to defaults on "ip link up"

[Greg Ungerer]

On 5/12/22 18:44, Rasmus Villemoes wrote:
> On 05/12/2022 08.15, Greg Ungerer wrote:
> > Hi Rasmus,
> >
> > On 23 Nov 2022, Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote:
> > > Currently, when a FEC device is brought up, the irq coalesce settings
> > > are reset to their default values (1000us, 200 frames). That's
> > > unexpected, and breaks for example use of an appropriate .link file to
> > > make systemd-udev apply the desired
> > > settings
> > > (https://www.freedesktop.org/software/systemd/man/systemd.link.html),
> > > or any other method that would do a one-time setup during early boot.
> > >
> > > Refactor the code so that fec_restart() instead uses
> > > fec_enet_itr_coal_set(), which simply applies the settings that are
> > > stored in the private data, and initialize that private data with the
> > > default values.
> > >
> > > Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> >
> > This breaks The ColdFire parts that use the FEC hardware module at the
> > very least. It results in an access to a register (FEC_TXIC0) that does
> > not exist in the ColdFire FEC. Reverting this change fixes it.
> >
> > So for me this is now broken in 6.1-rc8.
>
> Sorry about that.
>
> Since we no longer go through the same path that ethtool would, we need
> to add a check of the FEC_QUIRK_HAS_COALESCE bit before calling
> fec_enet_itr_coal_set() during initialization. So something like
>
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index 93a116788ccc..3df1b9be033f 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -1186,7 +1186,8 @@ fec_restart(struct net_device *ndev)
>                  writel(0, fep->hwp + FEC_IMASK);
>
>          /* Init the interrupt coalescing */
> -       fec_enet_itr_coal_set(ndev);
> +       if (fep->quirks & FEC_QUIRK_HAS_COALESCE)
> +               fec_enet_itr_coal_set(ndev);
>   }

That certainly fixes it.


> Or perhaps it's even better to do the check inside
> fec_enet_itr_coal_set() and just return silently?

That may well be better, yes.


> Either way, I don't know if it's too late to apply this fix, or if
> df727d4547 should just be reverted for 6.1 and then redone properly?
> Greg, can you check if the above fixes it for you?

Yep, that is good. I have no strong opinion on which way to handle
right now, so up to you.

Regards
Greg