linux-kernel - Re: [PATCH] clk: shmobile: div6: Avoid division by zero in .round

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Date:	Thu, 05 Feb 2015 19:19:14 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Ulrich Hecht <ulrich.hecht+renesas@...il.com>,
	Wolfram Sang <wsa@...g-engineering.com>,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: shmobile: div6: Avoid division by zero in .round_rate()

Hi Sergei,

On Thursday 05 February 2015 01:14:46 Sergei Shtylyov wrote:
> On 02/05/2015 01:04 AM, Sergei Shtylyov wrote:
> >>>>> Anyone may call clk_round_rate() with a zero rate value, so we have to
> >>>>> protect against that.
> >>>>> 
> >>>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> >>>> 
> >>>> Acked-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> >>>> 
> >>>> I agree that this should not be fixed in the core because the fixup is
> >>>> really driver dependant.
> >>>> 
> >>> Dunno, zero frequency seems generally insane to me.
> >> 
> >> It is useful to find the lowest frequency a clock can support. Basically
> >> it is a search for the floor frequency.
> >> 
> > Why not just use 1? Or are you assuming that some hardware could actually
> > support 0 Hz?
> 
> Replying to myself: yes, this has happened to me, when I forgot to override
> the EXTAL frequency in the board .dts file (default was 0).

So it was a good thing that the driver crashed, it let you find a bug ;-)

Jokes aside, a zero frequency is the usual way to find the lowest frequency, 
but I agree that there aren't many integers between 0 and 1. Mike, do you have 
an opinion ?

-- 
Regards,

Laurent Pinchart

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