netdev - Re: [Intel-wired-lan] [PATCH] igb: Report speed and duplex as unknown when device is runtime suspended

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Date:   Mon, 4 May 2020 11:47:08 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        "moderated list:INTEL ETHERNET DRIVERS" 
        <intel-wired-lan@...ts.osuosl.org>,
        "David S. Miller" <davem@...emloft.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH] igb: Report speed and duplex as unknown
 when device is runtime suspended

On Mon, May 4, 2020 at 10:32 AM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> igb device gets runtime suspended when there's no link partner. We can't
> get correct speed under that state:
> $ cat /sys/class/net/enp3s0/speed
> 1000
>
> In addition to that, an error can also be spotted in dmesg:
> [  385.991957] igb 0000:03:00.0 enp3s0: PCIe link lost
>
> Since device can only be runtime suspended when there's no link partner,
> we can directly report the speed and duplex as unknown.
>
> The more generic approach will be wrap get_link_ksettings() with begin()
> and complete() callbacks. However, for this particular issue, begin()
> calls igb_runtime_resume() , which tries to rtnl_lock() while the lock
> is already hold by upper ethtool layer.
>
> So let's take this approach until the igb_runtime_resume() no longer
> needs to hold rtnl_lock.
>
> Suggested-by: Alexander Duyck <alexander.duyck@...il.com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_ethtool.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_ethtool.c b/drivers/net/ethernet/intel/igb/igb_ethtool.c
> index 39d3b76a6f5d..b429bca4aa6a 100644
> --- a/drivers/net/ethernet/intel/igb/igb_ethtool.c
> +++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c
> @@ -143,6 +143,12 @@ static int igb_get_link_ksettings(struct net_device *netdev,
>         u32 speed;
>         u32 supported, advertising;
>
> +       if (pm_runtime_suspended(&adapter->pdev->dev)) {
> +               cmd->base.duplex = DUPLEX_UNKNOWN;
> +               cmd->base.speed = SPEED_UNKNOWN;
> +               return 0;
> +       }
> +
>         status = rd32(E1000_STATUS);
>         if (hw->phy.media_type == e1000_media_type_copper) {

The only thing I am not really a fan of with this approach is that it
is essentially discarding all of the information about what the user
has configured in terms of auto-negotiation, flow-control, etc.

>From what I can tell the only physical hardware interaction is the
read of the status register. Would it be possible to just initialize
the "status" value to 0, and then only perform the read of the
register if we are not runtime suspended?

Thanks.

- Alex