netdev - Re: [Issue report] drivers/ftgmac100: DHCP occasionally fails during boot up or link down/up

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Message-ID: <YgwSAjGN2eWUpamo@lunn.ch>
Date:   Tue, 15 Feb 2022 21:50:10 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Heyi Guo <guoheyi@...ux.alibaba.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Joel Stanley <joel@....id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Dylan Hung <dylan_hung@...eedtech.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Issue report] drivers/ftgmac100: DHCP occasionally fails during
 boot up or link down/up

On Tue, Feb 15, 2022 at 02:38:51PM +0800, Heyi Guo wrote:
> Hi,
> 
> We are using Aspeed 2600 and found DHCP occasionally fails during boot up or
> link down/up. The DHCP client is systemd 247.6 networkd. Our network device
> is 2600 MAC4 connected to a RGMII PHY module.
> 
> Current investigation shows the first DHCP discovery packet sent by
> systemd-networkd might be corrupted, and sysmtemd-networkd will continue to
> send DHCP discovery packets with the same XID, but no other packets, as
> there is no IP obtained at the moment. However the server side will not
> respond with this serial of DHCP requests, until it receives some other
> packets. This situation can be recovered by another link down/up, or a "ping
> -I eth0 xxx.xxx.xxx.xxx" command to insert some other TX packets.
> 
> Navigating the driver code ftgmac.c, I've some question about the work flow
> from link down to link up. I think the flow is as below:
> 
> 1. ftgmac100_open() will enable net interface with ftgmac100_init_all(), and
> then call phy_start()
> 
> 2. When PHY is link up, it will call netif_carrier_on() and then adjust_link
> interface, which is ftgmac100_adjust_link() for ftgmac100

The order there is questionable. Maybe it should first call the adjust
link callback, and then the netif_carrier_on(). However...

> 
> 3. In ftgmac100_adjust_link(), it will schedule the reset work
> (ftgmac100_reset_task)
> 
> 4. ftgmac100_reset_task() will then reset the MAC

Because of this delayed reset, changing the order will not help this
driver.

> I found networkd will start to send DHCP request immediately after
> netif_carrier_on() called in step 2, but step 4 will reset the MAC, which
> may potentially corrupt the sending packet.

What is not clear to my is why it is scheduling the work rather than
just doing it. At least for adjust_link, it is in a context it can
sleep. ftgmac100_set_ringparam() should also be able to
sleep. ftgmac100_interrupt() cannot sleep, so it does need to schedule
work.

I would suggest you refactor ftgmac100_reset_task() into a function
that actually does the reset, and a wrapper which takes a
work_struct. adjust_link can then directly do the reset, which
probably solves your problem.

	 Andrew