[alsa-devel] [PATCH] alsa-lib/tlv: fix handling of raw value ranges

[Takashi Iwai]

At Fri, 30 Mar 2012 13:44:43 +0200,
Takashi Iwai wrote:
> 
> At Fri, 30 Mar 2012 12:41:44 +0200 (CEST),
> Benoît Thébaudeau wrote:
> > 
> > Clemens Ladisch wrote:
> > > Benoît Thébaudeau wrote:
> > > > In case of a TLV dB range with all items having raw value ranges
> > > > strictly within
> > > > the main raw value range reported by the driver,
> > > > snd_tlv_convert_from_dB()
> > > > returned one of the main raw range boundaries, which was outside
> > > > all dB range
> > > > items.
> > >
> > > But the main raw range boundaries _are_ valid values.
> > 
> > Not always. For instance, if a codec register has the following volume values:
> > 0x00 to 0x20: prohibited
> > 0x21 to 0x40: some dB values
> > 0x41 to 0x60: prohibited
> > 0x61 to 0xff: some dB values
> 
> You can't prohibit the values that are exposed as accessible.
> The driver may return an error -EINVAL or such, but it doesn't mean
> that it's allowed to give a hole in the TLV dB definition.

But, don't get me wrong with the statement above.  Your fix can be an
improvement indeed.  The fact that the function relies on
range_min/max blindly isn't described anywhere, and it'd be better to
parse the range properly, of course, especially it's an exported
function, not only used as an internal function.

There may be minor coding issues as Clemens suggested, but they can be
easily fixed.

So, the motivation here is to make the code more robust and
consistent although the examples you raised seem like rather buggy
driver implementations.


Takashi