linux-kernel - Re: [PATCH v3 6/7] USB: ohci-at91: add usb_clk for transition to common clk framework

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Date:	Tue, 16 Jul 2013 14:47:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	boris brezillon <b.brezillon@...rkiz.com>
cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v3 6/7] USB: ohci-at91: add usb_clk for transition to
 common clk framework

On Tue, 16 Jul 2013, boris brezillon wrote:

> >> +	uclk = clk_get(&pdev->dev, "usb_clk");
> >> +	if (IS_ERR(uclk)) {
> >> +		uclk = NULL;
> >> +		dev_warn(&pdev->dev, "failed to get usb_clk\n");
> >> +	}
> > Is this really what you want for backward compatibility?
> Here are some proposition to remove the warning message:
> 
> 1) replace it with a dev_info and change the message:
>      dev_info(&pdev->dev, "failed to get usb_clk (most likely using old 
> at91 clk implementation)\n");
> 2) drop the log and silently ignore the missing clk (I'm not a big fan 
> of this solution
>      as it may lead to some errors if we're using new clk implem and the 
> clock is really missing)
> 3) rework the current clk_set_rate function to accept clk_set_rate on 
> usb clk and add clk_lookup entries
>      for the usb clk (I'm not a big fan of this solution neither as this 
> modifications will only be used for a short time
>      until the transition to common clk framework is completed).

Another possibility is to combine this change with the clock 
implementation update, and do them in a single patch.  Then backward 
compatibility would not be an issue.

Alan Stern

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