linux-kernel - Re: [PATCH] clk: Don't write error code into divider register

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Message-ID: <20170726082506.GC26726@tbergstrom-lnx.Nvidia.com>
Date:   Wed, 26 Jul 2017 11:25:06 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Stephen Boyd <sboyd@...eaurora.org>
CC:     Michael Turquette <mturquette@...libre.com>,
        <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Alex Frid <afrid@...dia.com>
Subject: Re: [PATCH] clk: Don't write error code into divider register

On Tue, Jul 25, 2017 at 05:32:08PM -0700, Stephen Boyd wrote:
> On 07/25, Peter De Schrijver wrote:
> > From: Alex Frid <afrid@...dia.com>
> > 
> > Add a check for error returned by divider value calculation to avoid
> > writing error code into hw register.
> > 
> > Signed-off-by: Alex Frid <afrid@...dia.com>
> > Reviewed-by: Peter De Schrijver <pdeschrijver@...dia.com>
> > Reviewed-by: Jon Mayo <jmayo@...dia.com>
> > ---
> 
> Fixes: bca9690b9426 ("clk: divider: Make generic for usage elsewhere")
> 
> perhaps?
> 
> Also, curious how this got triggered? Presumably round_rate would
> have failed before a set_rate call with something invalid came
> through so that's why nobody has reported anything so far.
> 

I don't really know. Aleks do you remember?

> >  drivers/clk/clk-divider.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> > index 9bb472c..4ed516c 100644
> > --- a/drivers/clk/clk-divider.c
> > +++ b/drivers/clk/clk-divider.c
> > @@ -385,12 +385,14 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
> >  				unsigned long parent_rate)
> >  {
> >  	struct clk_divider *divider = to_clk_divider(hw);
> > -	unsigned int value;
> > +	int value;
> >  	unsigned long flags = 0;
> >  	u32 val;
> >  
> >  	value = divider_get_val(rate, parent_rate, divider->table,
> >  				divider->width, divider->flags);
> > +	if (value < 0)
> 
> Perhaps value should be an s32 if we're doing a writel with it
> shifted so much. And then, we could declare it as a u32 and test
> it with
> 
> 	if ((s32)value < 0)
> 
> to see if there was an error. Sort of annoying that we've limited
> the available space of divider_get_val() by combining the value
> with the error code number space. We may want to not do that in
> case people have huge dividers.
> 

Yes. It would have been better to return the divider in a separate variable.
There seem to be few users though, only 6.

Peter.

> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project