linux-kernel - Re: [PATCH] usbnet: smsc95xx: simplify tx

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Date:   Sat, 06 Oct 2018 12:27:27 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, David.Laight@...lab.com, oneukum@...e.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel@...ts.codethink.co.uk
Subject: Re: [PATCH] usbnet: smsc95xx: simplify tx_fixup code



On 2018-10-05 22:24, David Miller wrote:
> From: Ben Dooks <ben.dooks@...ethink.co.uk>
> Date: Tue,  2 Oct 2018 17:56:02 +0100
> 
>> -	memcpy(skb->data, &tx_cmd_a, 4);
>> +	ptr = skb_push(skb, 8);
>> +	tx_cmd_a = cpu_to_le32(tx_cmd_a);
>> +	tx_cmd_b = cpu_to_le32(tx_cmd_b);
>> +	memcpy(ptr, &tx_cmd_a, 4);
>> +	memcpy(ptr+4, &tx_cmd_b, 4);
> 
> Even a memcpy() through a void pointer does not guarantee that gcc will
> not emit word sized loads and stores.
> 
> You must use the get_unaligned()/put_unaligned() facilities to do this
> properly.

Thanks, got a new version of the series just being tested with this.
Should it go into the original, or as a separate change?

> 
> I also agree that making a proper type and structure instead of using
> a void pointer would be better.