From: Andrew Lunn <andrew@lunn•ch>
To: Timur Tabi <timur@codeaurora•org>
Cc: "David S. Miller" <davem@davemloft•net>, netdev@vger•kernel.org
Subject: Re: [PATCH 1/2] [for 4.13] net: qcom/emac: disable flow control autonegotiation by default
Date: Wed, 2 Aug 2017 01:15:54 +0200 [thread overview]
Message-ID: <20170801231554.GA8415@lunn.ch> (raw)
In-Reply-To: <1501623460-3575-2-git-send-email-timur@codeaurora.org>
On Tue, Aug 01, 2017 at 04:37:39PM -0500, Timur Tabi wrote:
> The EMAC has a curious qwirk when RX flow control is enabled and the
> kernel hangs. With the kernel hung, the EMAC's RX queue soon fills.
> If RX flow control is enabled, the EMAC will then send a non-stop
> stream of pause frames until the system is reset. The EMAC does not
> have a built-in watchdog.
>
> In various tests, the pause frame stream sometimes overloads nearby
> switches, effectively disabling the network. Since the RX queue is
> large and the host processor is more than capable of handling incoming
> packets quickly, the only time the EMAC will send any pause frames is
> when the kernel is hung and unrecoverable.
>
> To avoid all these problems, we disable flow control autonegotiation
> by default, and only enable receiving pause frames.
>
> Cc: stable@vger•kernel.org # 4.11.x
> Signed-off-by: Timur Tabi <timur@codeaurora•org>
> ---
> drivers/net/ethernet/qualcomm/emac/emac.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/qualcomm/emac/emac.c b/drivers/net/ethernet/qualcomm/emac/emac.c
> index 60850bfa3d32..475c0ea29235 100644
> --- a/drivers/net/ethernet/qualcomm/emac/emac.c
> +++ b/drivers/net/ethernet/qualcomm/emac/emac.c
> @@ -441,8 +441,13 @@ static void emac_init_adapter(struct emac_adapter *adpt)
> /* others */
> adpt->preamble = EMAC_PREAMBLE_DEF;
>
> - /* default to automatic flow control */
> - adpt->automatic = true;
> + /* Disable transmission of pause frames by default, to avoid the
> + * risk of a pause frame flood that can occur if the kernel hangs.
> + * We still want to be able to respond to them, however.
> + */
> + adpt->automatic = false;
> + adpt->tx_flow_control = false;
> + adpt->rx_flow_control = true;
Hi Timur
Pause frames are something you can auto-negotiate at the PHY
level. Should you also be clearing some bits in the phydev, so the
peer knows pause frames are not supported?
Andrew
next prev parent reply other threads:[~2017-08-01 23:16 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-01 21:37 [PATCH 0/2] net: qcom/emac: fixes for pause frame floods Timur Tabi
2017-08-01 21:37 ` [PATCH 1/2] [for 4.13] net: qcom/emac: disable flow control autonegotiation by default Timur Tabi
2017-08-01 21:55 ` Florian Fainelli
2017-08-01 22:02 ` Timur Tabi
2017-08-01 22:08 ` Florian Fainelli
2017-08-01 23:15 ` Andrew Lunn [this message]
2017-08-02 0:56 ` Timur Tabi
2017-08-02 2:58 ` Andrew Lunn
2017-08-02 3:22 ` Timur Tabi
2017-08-02 13:48 ` David Laight
2017-08-02 14:21 ` Timur Tabi
2017-08-02 14:51 ` David Laight
2017-08-02 15:08 ` Timur Tabi
2017-08-02 15:38 ` David Laight
2017-08-02 17:54 ` David Miller
2017-08-02 18:23 ` Timur Tabi
2017-08-02 18:35 ` David Miller
2017-08-02 18:39 ` Timur Tabi
2017-08-02 23:15 ` David Miller
2017-08-03 1:00 ` Timur Tabi
2017-08-02 18:36 ` David Miller
2017-08-01 21:37 ` [PATCH 2/2] net: qcom/emac: add software control for pause frame mode Timur Tabi
2017-08-01 21:51 ` Florian Fainelli
2017-08-01 22:00 ` Timur Tabi
2017-08-01 22:06 ` Florian Fainelli
2017-09-12 22:07 ` Timur Tabi
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