netdev - RE: [PATCH net-next,V2] Add LAN9352 Ethernet Driver

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Message-ID: <90A7E81AE28BAE4CBDDB3B35F187D264402EF62A@CHN-SV-EXMX02.mchp-main.com>
Date:	Fri, 12 Feb 2016 19:10:52 +0000
From:	<Bryan.Whitehead@...rochip.com>
To:	<LinoSanfilippo@....de>, <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>
Subject: RE: [PATCH net-next,V2] Add LAN9352 Ethernet Driver

Lino,

Regarding "a matching smp_rmb() in the irq handler"
There is a smp_wmb() in the irq handler, since in both cases we are forcing a write operation on software_irq_signal.

I suppose using atomic operations on software_irq_signal would also work, but this driver was based on 
drivers/net/ethernet/smsc/smsc911x.c
And if possible I'd prefer to keep logical changes to a minimum.
Plus this is not a "read modify write" scenario so I think the memory barrier is sufficient.
Do you agree?

Regarding register_netdev.
I'll move register_netdev till after the mac address is set.

Thanks,
Bryan

-----Original Message-----
From: Lino Sanfilippo [mailto:LinoSanfilippo@....de] 
Sent: Thursday, February 11, 2016 7:14 PM
To: Bryan Whitehead - C21958; davem@...emloft.net
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next,V2] Add LAN9352 Ethernet Driver

Hi,

> +static int mchp9352_open(struct net_device *dev) {

> +
> +	MCHP_TRACE(pdata, ifup, "Testing irq handler using IRQ %d", dev->irq);
> +	pdata->software_irq_signal = 0;
> +
> +	/* Testing irq handler */
> +	smp_wmb();

Should not there at least be a matching smp_rmb() in the irq handler?
Maybe an atomic_t would be a better choice for a flag like software_irq_signal here.

> +
> +static int mchp9352_drv_probe(struct platform_device *pdev)

> +
> +	netif_carrier_off(dev);
> +
> +	retval = register_netdev(dev);
> +	if (retval) {
> +		MCHP_WARN(pdata, probe, "Error %i registering device", retval);
> +		goto out_free_irq;
> +	} else {
> +		MCHP_TRACE(pdata, probe,
> +			   "Network interface: \"%s\"", dev->name);
> +	}

Note that as soon as the network device is registered "open" may be called so everything should be set up already. In this case the mac address (dev->dev_addr) is accessed in open but may not yet contain valid data when register_netdev is called.

Regards,
Lino