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

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Message-ID: <86d17574-926a-e449-47ce-409701e80656@westnet.com.au>
Date:   Mon, 5 Dec 2022 23:15:15 +1000
From:   Greg Ungerer <gregungerer@...tnet.com.au>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Joakim Zhang <qiangqing.zhang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: fec: don't reset irq coalesce settings to defaults
 on "ip link up"


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@...musvillemoes.dk> 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@...musvillemoes.dk>
>>
>> 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