netdev - Re: [PATCH ethtool] sfc: Add support for EF10 registers

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Message-ID: <1379955122.2485.47.camel@bwh-desktop.uk.level5networks.com>
Date:	Mon, 23 Sep 2013 17:52:02 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	<netdev@...r.kernel.org>, <linux-net-drivers@...arflare.com>
Subject: Re: [PATCH ethtool] sfc: Add support for EF10 registers

On Mon, 2013-09-23 at 17:14 +0100, David Laight wrote:
> >  struct efx_nic_reg_field {
> >  	const char *name;
> >  	u32 lbn:7, width:8;
> > -	u32 min_revision:2, max_revision:2;
> > +	u32 min_revision:3, max_revision:3;
> >  };
> ...
> >  struct efx_nic_reg_table {
> >  	const char *name;
> >  	const struct efx_nic_reg_field *fields;
> >  	u32 field_count:7;
> > -	u32 min_revision:2, max_revision:2;
> > +	u32 min_revision:3, max_revision:3;
> >  	u32 step:6, rows:21;
> >  };
> 
> These bitfields look rather pointless.
> AFACT the size of the structures wouldn't change if the fields
> were just u8 or u32. The code would be a lot smaller.

The definition of struct efx_nic_reg_table is based on the structure of
the same name in the driver, where I think the bitfields do provide a
net saving (but I'm not sure).  efx_nic_reg_field is specific to ethtool
and the bitfields there are indeed pointless.

Changing to u8 and u32 as appropriate saved about 200 bytes on an x86_64
build here.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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