netdev - RE: [PATCH, resubmit] ax88179_178a: ASIX AX88179_178A USB 3.0/2.0 to gigabit ethernet adapter driver

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Date:	Fri, 8 Feb 2013 10:23:08 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Ben Hutchings" <bhutchings@...arflare.com>,
	"Freddy Xin" <freddy@...x.com.tw>
Cc:	<netdev@...r.kernel.org>, <davem@...emloft.net>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH, resubmit] ax88179_178a: ASIX AX88179_178A USB 3.0/2.0 to gigabit ethernet adapter driver

> > +struct ax88179_rx_pkt_header {
> > +	u8	l4_csum_err:1,
> > +		l3_csum_err:1,
> > +		l4_type:3,
> > +		l3_type:2,
> > +		ce:1;
> > +
> > +	u8	vlan_ind:3,
> > +		rx_ok:1,
> > +		pri:3,
> > +		bmc:1;
> > +
> > +	u16	len:13,
> > +		crc:1,
> > +		mii:1,
> > +		drop:1;
> > +} __packed;
> 
> This won't work on both big-endian systems (assuming this works on x86).
> You apparently try to convert the structure in-place in
> ax88179_rx_fixup() by calling le32_to_cpus(); that may work if you
> define all the bitfields to be part of a u32 but it won't work with the
> current definition.

Trying to use bit fields to map hardware registers (etc) isn't a
good idea at all. The C standard says absolutely nothing about
the order in which the bits are allocated to the field names.
(There are at least 4 possible orederings.)

It is much better to define constants for the bit values and
explicitly mask them as required.

	David