linux-kernel - Re: [PATCH V8 12/13] ptp: Added a clock driver for the IXP46x.

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Date:	Sat, 08 Jan 2011 17:25:36 +0100
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	John Stultz <johnstul@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V8 12/13] ptp: Added a clock driver for the IXP46x.

Richard Cochran <richardcochran@...il.com> writes:

> The time stamp code clones the skb, but the LE version frees the skb
> too early. Perhaps we can move that dev_kfree_skb(skb) in the LE case
> to be the last statement in eth_xmit(). What do you think?

I think so. Or something similar.

> Do you mean, you don't like the constant on the left hand side?

Yes.

> Is that prohibited by CodingStyle or similar?

I don't think so. It's just a personal taste. I think it's based on
things learned in primary school, they teach to write (comparisons)
X = 4 instead of the other way around, and my brain seems to shock
a bit on the opposite.

> I got into the habit of writing it that way to prevent a typo like:
>
> 	if (irq = NO_IRQ)

I see. Unfortunately it doesn't prevent typos like this when the right
side isn't a constant. Anyway gcc warns about them, even when both sides
are variable.

>> Also I don't like the ixp_read/ixp_write() trivial macros. Why not
>> simply call __raw_readl() and __raw_writel()?
>
> Well, I have had the experience back in 2.4 days of having my drivers
> ruined by the changing IO macros in the kernel. The wrappers are
> supposed to help if that ever happens again. Seeing *two* leading
> underscores in the macro names certainly makes me nervous.

Well, these two underscores mainly mean it's arch-dependent, but so are
the ixp4xx drivers. Using the __raw_read* directly is the preferred
method (or, perhaps, in such case, it's the only way).

Actually, I was thinking about changing the macros some time ago, and it
may eventually happen. But we'll fix all the code using them then.
-- 
Krzysztof Halasa
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