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Date: Wed, 26 Feb 2003 16:37:34 +0100 (MET)
From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Jeff Garzik <jgarzik@pobox.com>
cc: Marcus Meissner <meissner@suse.de>, "David S. Miller" <davem@redhat.com>,
       Linux Kernel Development <linux-kernel@vger.kernel.org>,
       engebret@us.ibm.com
Subject: Re: [PATCH] fixed pcnet32 multicast listen on big endian
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On Wed, 26 Feb 2003, Jeff Garzik wrote:
> Geert Uytterhoeven wrote:
> > On Sun, 23 Feb 2003, Geert Uytterhoeven wrote:
> >>On Wed, 5 Feb 2003, Marcus Meissner wrote:
> >>>This fixes multicast listen for pcnet32 on at least powerpc and powerpc64
> >>>kernels.
> >>>
> >>>The mcast_table is in memory referenced by the card and so it needs
> >>>to be accessed in little endian mode.
> >>>
> >>>Ciao, Marcus
> >>>
> >>>--- linux-2.4.19/drivers/net/pcnet32.c.be	2003-02-05 07:59:27.000000000 +0100
> >>>+++ linux-2.4.19/drivers/net/pcnet32.c	2003-02-05 08:00:22.000000000 +0100
> >>>@@ -1534,7 +1534,9 @@
> >>> 	
> >>> 	crc = ether_crc_le(6, addrs);
> >>> 	crc = crc >> 26;
> >>>-	mcast_table [crc >> 4] |= 1 << (crc & 0xf);
> >>>+	mcast_table [crc >> 4] = le16_to_cpu(
> >>
> >>                                 ^^^^^^^^^^^
> >>
> >>>+		le16_to_cpu(mcast_table [crc >> 4]) | (1 << (crc & 0xf))
> >>>+	);
> >>
> >>Shouldn't the first conversion be `cpu_to_le16'?
> > 
> > 
> > Ugh, a quick grep shows that this driver _always_ uses `le*_to_cpu()' to
> > convert from CPU to little endian.
> 
> Cosmetically you are correct, and I prefer it to be changed eventually.
> 
> However programatically, it has no effect, because those cpu_to_foo and 
> foo_to_cpu functions either swap, or they don't.  Direction doesn't 
> matter terribly much :)

That's true.

BTW, you save one swap by changing the code to

    mcast_table [crc >> 4] |= cpu_to_le16(1 << (crc & 0xf));

Because the order of bitwise or and swap doesn't matter.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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