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From: "Ardelean, Alexandru" <alexandru.Ardelean@analog.com>
To: "andriy.shevchenko@linux.intel.com"  <andriy.shevchenko@linux.intel.com>
Cc: "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jic23@kernel.org" <jic23@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"lars@metafoo.de" <lars@metafoo.de>
Subject: Re: [PATCH 3/3][V3] iio: Handle enumerated properties with gaps
Date: Fri, 5 Jul 2019 13:35:14 +0000	[thread overview]
Message-ID: <97a28b3d5a36886ca7980d56911fadcc2ddbb0c1.camel@analog.com> (raw)
In-Reply-To: <780a4bcbf2e8a2d816efe2ed9613ac2b1594282e.camel@analog.com>

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
> > 
> > 

  reply	other threads:[~2019-07-05 14:52 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08 11:19 [PATCH 1/3][V3] lib: fix __sysfs_match_string() helper when n != -1 Alexandru Ardelean
2019-05-08 11:19 ` [PATCH 2/3][V3] scsi: sd: remove sysfs_match_string() dense array comment Alexandru Ardelean
2019-05-08 11:19 ` [PATCH 3/3][V3] iio: Handle enumerated properties with gaps Alexandru Ardelean
2019-05-08 13:17   ` Andy Shevchenko
2019-05-09  7:31     ` Ardelean, Alexandru
2019-07-05 13:35       ` Ardelean, Alexandru [this message]
2019-05-28  7:18 ` [PATCH 1/3][V3] lib: fix __sysfs_match_string() helper when n != -1 Ardelean, Alexandru
2019-06-25 13:01 ` [PATCH][V4] " Alexandru Ardelean
2019-06-25 13:28   ` Andy Shevchenko
2019-06-25 19:42     ` Andrew Morton
2019-06-26  7:57       ` Ardelean, Alexandru
2019-07-14 10:12 ` [PATCH 1/3][V3] " Jonathan Cameron

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