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    SubjectRe: [PATCH 3/3][V3] iio: Handle enumerated properties with gaps
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    On Thu, 2019-05-09 at 10:31 +0300, Alexandru Ardelean wrote:
    > On Wed, 2019-05-08 at 16:17 +0300, Andy Shevchenko wrote:
    > > [External]
    > >
    > >
    > > On Wed, May 08, 2019 at 02:19:13PM +0300, Alexandru Ardelean wrote:
    > > > From: Lars-Peter Clausen <lars@metafoo.de>
    > > >
    > > > Some enums might have gaps or reserved values in the middle of their
    > > > value
    > > > range. E.g. consider a 2-bit enum where the values 0, 1 and 3 have a
    > > > meaning, but 2 is a reserved value and can not be used.
    > > >
    > > > Add support for such enums to the IIO enum helper functions. A reserved
    > > > values is marked by setting its entry in the items array to NULL rather
    > > > than the normal descriptive string value.
    > > >
    > > > Also, `__sysfs_match_string()` now supports NULL gaps, so that doesn't
    > > > require any changes.
    > > > - for (i = 0; i < e->num_items; ++i)
    > > > + for (i = 0; i < e->num_items; ++i) {
    > > > + if (!e->items[i])
    > > > + continue;
    > > > len += scnprintf(buf + len, PAGE_SIZE - len, "%s ", e-
    > > > > items[i]);
    > > > + }
    > >
    > > The problem here that the user will have no clue where the gap is
    > > happened, to
    > > solve this we need either bitmap of array, where set bits shows defined
    > > items,
    > > or use comma-separated list of values. The latter would need another node
    > > since
    > > we don't break user space.
    >
    > Hmmm.
    > I am wondering if there are cases where userspace would care about reserved
    > values and/or positions of reserved bit-fields.
    > Maybe you could offer examples/use-cases where this is needed.
    >
    > To some extent the kernel [drivers & frameworks] should probably not need
    > to expose that "string-enum-X" == `bitfield_2` matching; otherwise it
    > doesn't really add much value ; the whole point of frameworks [in general]
    > is to offer some level of abstraction to HW.
    >
    > The only example I can think of [atm], is when a reserved bit-field will be
    > used in the future. But then, the driver should care about this, and not
    > the framework. The driver should decide that "bitfield_2" will
    > enable/disable something [in the future], and should be considered in a
    > such a way (when being written). If the driver can't make this prediction [
    > about "bitfield_2"] then a new driver must be written anyway.
    >
    > But I will agree that I may not have all arguments in mind to be 100% sure
    > of all this.
    >

    Hey,

    Is there any feedback/counter-arguments for this?

    Thanks
    Alex


    > Thanks
    > Alex
    >
    > > --
    > > With Best Regards,
    > > Andy Shevchenko
    > >
    > >
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