Re: [Linux-kernel] [net-next, 2/5] sh_eth: WARN on access to a register not implemented in a particular chip

From: Ben Dooks <ben.dooks@codethink•co.uk>
To: Ben Hutchings <ben.hutchings@codethink•co.uk>,
	Geert Uytterhoeven <geert@linux-m68k•org>
Cc: linux-kernel@lists•codethink.co.uk,
	Yoshihiro Kaneko <ykaneko0929@gmail•com>,
	Sergei Shtylyov <sergei.shtylyov@cogentembedded•com>,
	Mitsuhiro Kimura <mitsuhiro.kimura.kc@renesas•com>,
	netdev@vger•kernel.org,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas•com>,
	Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas•com>,
	"David S. Miller" <davem@davemloft•net>
Subject: Re: [Linux-kernel] [net-next, 2/5] sh_eth: WARN on access to a register not implemented in a particular chip
Date: Mon, 09 Mar 2015 08:50:24 +0000	[thread overview]
Message-ID: <54FD5ED0.6070208@codethink.co.uk> (raw)
In-Reply-To: <1425561532.4288.34.camel@xylophone.i.decadent.org.uk>

On 05/03/15 13:18, Ben Hutchings wrote:
> On Thu, 2015-03-05 at 10:02 +0100, Geert Uytterhoeven wrote:
>> Replying to a patchwork mbox, as I noticed this is in net-next.
>>
>> On Thu, 26 Feb 2015, Ben Hutchings wrote:
>>> Currently we may silently read/write a register at offset 0.  Change
>>> this to WARN and then ignore the write or read-back all-ones.
>>>
>>> Signed-off-by: Ben Hutchings <ben.hutchings@codethink•co.uk>
>>> Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded•com>
>>
>> While this may be a good idea for debugging...
>>
>>> --- a/drivers/net/ethernet/renesas/sh_eth.h
>>> +++ b/drivers/net/ethernet/renesas/sh_eth.h
>>> @@ -543,19 +543,29 @@ static inline void sh_eth_soft_swap(char *src, int len)
>>>  #endif
>>>  }
>>>  
>>> +#define SH_ETH_OFFSET_INVALID	((u16) ~0)
>>> +
>>>  static inline void sh_eth_write(struct net_device *ndev, u32 data,
>>>  				int enum_index)
>>>  {
>>>  	struct sh_eth_private *mdp = netdev_priv(ndev);

does de-referencing this each time make a difference? Looks like
it would have been easier to pass an "struct sh_eth_private" instead
of the "struct net_device *ndev"

>>> +	u16 offset = mdp->reg_offset[enum_index];
>>> +
>>> +	if (WARN_ON(offset == SH_ETH_OFFSET_INVALID))
>>> +		return;

You could cange the mdp->reg_offset to an mdp->reg_pointer and make
any invalid registers a NULL. This would at-least make it fail on an
invalid access.

>> ... adding WARN_ON() to static inline functions increases code size a lot:
>>
>> $ size drivers/net/ethernet/renesas/sh_eth.o{.orig,}
>>    text	   data	    bss	    dec	    hex	filename
>>   23352	   1136	      0	  24488	   5fa8	drivers/net/ethernet/renesas/sh_eth.o.orig
>>   27225	   1136	      0	  28361	   6ec9	drivers/net/ethernet/renesas/sh_eth.o
>> $
> 
> Time to un-inline it, maybe?
> 
> Ben.
> 
> 
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-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius