linux-kernel - Re: [PATCH RFC] clk: divider: Tolerate 0 divider for one based dividers

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Date:	Mon, 1 Apr 2013 11:31:32 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Mike Turquette <mturquette@...aro.org>
CC:	Shawn Guo <shawn.guo@...aro.org>, Rajendra Nayak <rnayak@...com>,
	Andrew Lunn <andrew@...n.ch>,
	James Hogan <james.hogan@...tec.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] clk: divider: Tolerate 0 divider for one based
 dividers

Hi Mike,

On Mon, Apr 01, 2013 at 11:25:22AM -0700, Mike Turquette wrote:
> Quoting Sören Brinkmann (2013-03-22 11:00:15)
> > Since some of our dividers have a reset value of 0, I see this warning
> > during boot up. My intention here is to get rid of the warning for clocks
> > which deem 0 a valid divider value.
> > I thought, reusing the ONE_BASED flag might be okay, since all such
> > dividers have this redundant 0 state and might handle it similar.
> > Otherwise a new flag might be required.
> > 
> 
> Hi Soren,
> 
> A flag will be necessary.  I just checked some documentation for the
> divider outputs for OMAP's PLLs and (which use the common clk_divider
> type) and programming zero into those dividers is not allowed.  At reset
> the divider registers are set to 1.
> 
> So it is unsafe to simply reuse the ONE_BASED flag.
> 
> Let's keep the current behavior as the default and introduce a new flag
> to handle the special case of a zero divider.  Would you like to take a
> crack at it?  It might also be nice to update the WARN message with a
> hint to take a look at your new flag in case future platforms hit the
> same issue as you.
Okay, sounds good. I should be able to get something ready within this
week.
Does anybody have suggestions for naming the new flag?
CLK_DIVIDER_ZERO_OKAY was my original suggestionn I think.

	Sören


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