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SubjectRe: [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@nvidia.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@nvidia.com>
> > Reviewed-by: Peter De Schrijver <pdeschrijver@nvidia.com>
> > Reviewed-by: Jon Mayo <jmayo@nvidia.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

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