Re: [PATCH v6 4/6] lib/linear_ranges: Add linear_range_get_selector_high_array

[Amit Sunil Dhamne]

On 2/16/26 5:58 AM, Matti Vaittinen wrote:
> On 14/02/2026 05:12, Amit Sunil Dhamne via B4 Relay wrote:
> > From: Amit Sunil Dhamne <amitsd@xxxxxxxxxx>
> >
> > Add a helper function to find the selector for a given value in a linear
> > range array. The selector should be such that the value it represents
> > should be higher or equal to the given value.
> >
> > Signed-off-by: Amit Sunil Dhamne <amitsd@xxxxxxxxxx>
> > ---
> >   include/linux/linear_range.h |  3 +++
> >   lib/linear_ranges.c          | 36 ++++++++++++++++++++++++++++++++++++
> >   2 files changed, 39 insertions(+)
> >
> > diff --git a/include/linux/linear_range.h b/include/linux/linear_range.h
> > index 2e4f4c3539c0..0f3037f1a94f 100644
> > --- a/include/linux/linear_range.h
> > +++ b/include/linux/linear_range.h
> > @@ -57,5 +57,8 @@ void linear_range_get_selector_within(const struct 
> > linear_range *r,
> >   int linear_range_get_selector_low_array(const struct linear_range *r,
> >                       int ranges, unsigned int val,
> >                       unsigned int *selector, bool *found);
> > +int linear_range_get_selector_high_array(const struct linear_range *r,
> > +                     int ranges, unsigned int val,
> > +                     unsigned int *selector, bool *found);
> >     #endif
> > diff --git a/lib/linear_ranges.c b/lib/linear_ranges.c
> > index a1a7dfa881de..c85583678f6b 100644
> > --- a/lib/linear_ranges.c
> > +++ b/lib/linear_ranges.c
> > @@ -241,6 +241,42 @@ int linear_range_get_selector_high(const struct 
> > linear_range *r,
> >   }
> >   EXPORT_SYMBOL_GPL(linear_range_get_selector_high);
> >   +/**
> > + * linear_range_get_selector_high_array - return linear range 
> > selector for value
> > + * @r:        pointer to array of linear ranges where selector is 
> > looked from
> > + * @ranges:    amount of ranges to scan from array
> > + * @val:    value for which the selector is searched
> > + * @selector:    address where found selector value is updated
> > + * @found:    flag to indicate that given value was in the range
> > + *
> > + * Scan array of ranges for selector for which range value matches 
> > given
> > + * input value. Value is matching if it is equal or higher than 
> > given value
> > + * If given value is found to be in a range scanning is stopped and 
> > @found is
> > + * set true. If a range with values greater than given value is found
> > + * but the range min is being greater than given value, then the 
> > range's
> > + * lowest selector is updated to @selector and scanning is stopped.
>
> Is there a reason why the scanning is stopped here? What ensures that 
> the rest of the ranges wouldn't contain a better match?
>
> The logic is now different from the 
> linear_range_get_selector_low_array(), and I would like to understand 
> why? It'd be nice if these APIs were 'symmetric' to avoid confusion. 
> Hence, I would like to know rationale behind making them different.


The rationale for this being asymmetric is to find the tightest upper 
bound for `value` < minimum value across the linear range array.

To better illustrate this with an example. I have 2 entries in the 
linear range array [ [4, 8], [11, 15] ]. Let's assume I pass a value of "2".

Based on my current approach, the call to get_selector_high() would 
successfully return with `found`=false and a selector value 
corresponding to "4".

However, if I continued to search, I would end up the selector 
corresponding to "11". A selector corresponding to "4" is much 
closer/tighter than "2".

For values higher than the highest value in any range, this would keep 
iterating and end up returning an -EINVAL.

For in range values this would work as expected.

This implementation assumes that the linear ranges are provided in 
sorted order, an assumption that I believe already underlies the 
existing *_low_array() logic.


Regards,

Amit

> > + *
> > + * Return: 0 on success, -EINVAL if range array is invalid or does 
> > not contain
> > + * range with a value greater or equal to given value
> > + */
> > +int linear_range_get_selector_high_array(const struct linear_range *r,
> > +                     int ranges, unsigned int val,
> > +                     unsigned int *selector, bool *found)
> > +{
> > +    int i;
> > +    int ret;
> > +
> > +    for (i = 0; i < ranges; i++) {
> > +        ret = linear_range_get_selector_high(&r[i], val, selector,
> > +                             found);
> > +        if (!ret)
> > +            return 0;
> > +    }
> > +
> > +    return -EINVAL;
> > +}
> > +EXPORT_SYMBOL_GPL(linear_range_get_selector_high_array);
> > +
> >   /**
> >    * linear_range_get_selector_within - return linear range selector 
> > for value
> >    * @r:        pointer to linear range where selector is looked from