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

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Date:	Wed, 10 Aug 2016 10:49:24 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Timur Tabi <timur@...eaurora.org>,
	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

On 08/10/2016 09:38 AM, Timur Tabi wrote:
> 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.

Whatever emac_mac_down() does you can unroll it in the change_mtu
callback anyway, so if this a problematic sequence you can work around it.

> 
> 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.

Buf if this is really what you copy/pasted here, why do this twice anyway?

> 
> 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.
> 

Not clear how the two relate with each other here, must be specific to
your driver implementation somehow.
-- 
Florian