From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Mike Turquette <mturquette@linaro.org>, Wolfram Sang <wsa@the-dreams.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Ulrich Hecht <ulrich.hecht+renesas@gmail.com>,
        Wolfram Sang <wsa@sang-engineering.com>, linux-sh@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] clk: shmobile: div6: Avoid division by zero in .round_rate()
Date: Thu, 05 Feb 2015 19:19:14 +0200
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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@glider.be>
> >>>> 
> >>>> Acked-by: Wolfram Sang <wsa+renesas@sang-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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