linux-kernel - Re: [PATCH] USB: ohci-at91: add usb_clk for transition to common clk framework

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Message-ID: <Pine.LNX.4.44L0.1308011153180.1534-100000@iolanthe.rowland.org>
Date:	Thu, 1 Aug 2013 11:56:09 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	boris brezillon <b.brezillon@...rkiz.com>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] USB: ohci-at91: add usb_clk for transition to common
 clk framework

On Thu, 1 Aug 2013, boris brezillon wrote:

> > What happens if uclk isn't found but it is needed?
> It will not fail but I guess the usb host won't work as the clock won't 
> be correctly
> configured.
> 
> I agree with you: this is not a good solution.
> 
> Another option is to keep the previous version of this patch and put 
> uclk handling
> in "#ifdef CONFIG_COMMON_CLK #endif" sections.
> 
> Would this be acceptable ?

Yes.  However, a more elegant approach is to protect the relevant 
statements with: if (defined(CONFIG_COMMON_CLK)).  This preprocessor 
evaluates this to a 0 or 1, so the compiler will not generate output 
for the protected source code if the symbol isn't defined.

Alan Stern

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