netdev - Re: [PATCH] [v7] net: emac: emac gigabit ethernet controller driver

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Date:	Wed, 10 Aug 2016 11:38:53 -0500
From:	Timur Tabi <timur@...eaurora.org>
To:	Florian Fainelli <f.fainelli@...il.com>,
	Lino Sanfilippo <LinoSanfilippo@....de>,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, sdharia@...eaurora.org,
	shankerd@...eaurora.org, vikrams@...eaurora.org,
	cov@...eaurora.org, gavidov@...eaurora.org, robh+dt@...nel.org,
	andrew@...n.ch, bjorn.andersson@...aro.org, mlangsdo@...hat.com,
	jcm@...hat.com, agross@...eaurora.org, davem@...emloft.net
Subject: Re: [PATCH] [v7] net: emac: emac gigabit ethernet controller driver

Florian Fainelli wrote:
>> >Is there an easy way for me to stop the RX path before I set rxbuf_size?
>> >  Some netif_xxx function I can call?
> napi_disable() should take care of that.

It appears that if I call netif_stop_queue() *afer* calling 
napi_disable(), I get a hang and/or TX timeout.  Since emac_mac_down() 
does this:

	netif_stop_queue(netdev);
	napi_disable(&adpt->rx_q.napi);

I cannot call just napi_disable() in emac_change_mtu(), because when I 
then call emac_mac_down(), the first thing it does is call 
netif_stop_queue(), and that's when I timeout/hang.

Unfortunately, I cannot even do this:

	netif_stop_queue(netdev);
	napi_disable(&adpt->rx_q.napi);
	netif_stop_queue(netdev);
	napi_disable(&adpt->rx_q.napi);

Even though I've already called netif_stop_queue(), calling it again 
causes the timeout/hang.

Is this expected?  I never understood why I needed to call 
netif_stop_queue() before napi_disable().  I do see some drivers do not 
call netif_stop_queue().  I even saw a driver that calls them in reverse 
order, so I don't understand why that sequence breaks for me but not him.

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