netdev - Re: [PATCH] drivers/net/usb/asix: resync from vendor's copy

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Message-ID: <4EBABAFD.6050604@teksavvy.com>
Date:	Wed, 09 Nov 2011 12:40:13 -0500
From:	Mark Lord <kernel@...savvy.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/net/usb/asix:  resync from vendor's copy

On 11-11-09 12:31 PM, Ben Hutchings wrote:
> On Wed, 2011-11-09 at 12:20 -0500, Mark Lord wrote:
>> On 11-11-09 11:57 AM, Mark Lord wrote:
>>> On 11-11-09 11:47 AM, Mark Lord wrote:
>>> ..
>>>> Note:  I'm looking at smsc95xx.c and smsc75xx.c for examples,
>>>> and they both have the same problem I'll have here:
>>>>
>>>> How to update the csum settings atomically.
>>>> A spinlock is no good, because config register access is over USB.
>>>
>>> Nevermind.. a slight change in the logic and all is well again.
>> ..
>>
>> Or even simpler (below).  I don't think this method requires any
>> extra locking, but I'm still open to persuasion.  :)
> 
> Looks reasonable, but...
> 
>> static int ax88772b_set_features(struct net_device *netdev, u32 features)
>> {
>>         struct usbnet *dev = netdev_priv(netdev);
>>         struct ax88772b_data *priv = (struct ax88772b_data *)dev->driver_priv;
>>         u16 tx_csum = 0, rx_csum = 0;
>>
>>         priv->features = features & (NETIF_F_HW_CSUM | NETIF_F_RXCSUM);
> 
> ...why do you need priv->features at all?


There's code elsewhere that takes action under some conditions
based on the current setting of the NETIF_F_RXCSUM flag.

I don't claim to fully understand what's going on,
but it doesn't care much about races on set/clear of the flag.

Cheers
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