Subject: [PATCH 1/8] clk: sunxi: factors: Add m_start parameters

From: [email-masked] (Maxime Ripard)
Date: Fri, 15 May 2015 10:05:46 +0200

On Fri, May 15, 2015 at 03:48:38PM +0800, Chen-Yu Tsai wrote:
> On Fri, May 15, 2015 at 3:43 PM, Maxime Ripard
> <[email-masked]> wrote:
> > On Thu, May 14, 2015 at 05:12:07PM +0800, Chen-Yu Tsai wrote:
> >> On Sat, May 2, 2015 at 7:24 PM, Maxime Ripard
> >> <[email-masked]> wrote:
> >> > Some clocks start incrementing the m factor at 0. Add a parameter to handle
> >> > it just like we did for the N factor.
> >> >
> >> > Since the behaviour until now was to assume that the m factor was starting
> >> > at 1, we also need to fix the other users.
> >> >
> >> > Signed-off-by: Maxime Ripard <[email-masked]>
> >> > ---
> >> >  drivers/clk/sunxi/clk-factors.c    | 11 ++++++++++-
> >> >  drivers/clk/sunxi/clk-factors.h    |  2 ++
> >> >  drivers/clk/sunxi/clk-mod0.c       |  2 ++
> >> >  drivers/clk/sunxi/clk-sun8i-mbus.c |  2 ++
> >> >  drivers/clk/sunxi/clk-sun9i-core.c |  6 ++++++
> >> >  drivers/clk/sunxi/clk-sunxi.c      | 10 ++++++++++
> >> >  6 files changed, 32 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/drivers/clk/sunxi/clk-factors.c b/drivers/clk/sunxi/clk-factors.c
> >> > index 8c20190a3e9f..100a711c3e3d 100644
> >> > --- a/drivers/clk/sunxi/clk-factors.c
> >> > +++ b/drivers/clk/sunxi/clk-factors.c
> >> > @@ -56,15 +56,24 @@ static unsigned long clk_factors_recalc_rate(struct clk_hw *hw,
> >> >         /* Get each individual factor if applicable */
> >> >         if (config->nwidth != SUNXI_FACTORS_NOT_APPLICABLE)
> >> >                 n = FACTOR_GET(config->nshift, config->nwidth, reg);
> >> > +
> >> >         if (config->kwidth != SUNXI_FACTORS_NOT_APPLICABLE)
> >> >                 k = FACTOR_GET(config->kshift, config->kwidth, reg);
> >> > +
> >> >         if (config->mwidth != SUNXI_FACTORS_NOT_APPLICABLE)
> >> >                 m = FACTOR_GET(config->mshift, config->mwidth, reg);
> >> > +       else
> >> > +               /* Make sure we don't get a division by zero */
> >> > +               m = 1;
> >>
> >> What happens when mwidth is valid, m_start = 0, and m = 0?
> >
> > That's a very good question. A division by zero in the kernel, I'd
> > say.
> >
> > But I don't think we can end up in such a case today, and it's
> > somewhat expected that it will happen, and no clock have looked at can
> > actually end up in such a case.
> 
> It's possible if the bootloader left the clock in an invalid state.
> How about just returning 0, indicating an invalid rate, early?

The value set in the register might be zero, but that will always
really mean 1, either through m_start or m_zero. That would be a bug
in the driver itself.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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