At Mon, 04 Sep 2006 13:40:13 +0100,
James Courtier-Dutton wrote:
>
> Takashi Iwai wrote:
> > Hi,
> >
> > I found that some hardwares require the combination of dB scale
> > ranges. For example, es1938 has volume controls with two curves,
> > e.g. the volume step in the value 0-8 is 3 dB while it's 1.5 dB in the
> > values 8-15.
> >
> > The patch below introduces a new TLV type, DB_RANGE, to implement
> > the compound dB scales. It can contain one or more child TLVs,
> > together with min and max values for each.
> >
> > The first patch is for the kernel and the second for alsa-lib.
> >
> > Any comments?
> >
> >
> > Takashi
> >
> +static int do_convert_to_dB(unsigned int *tlv, long rangemin, long
> rangemax,
> + long volume, long *db_gain)
> +{
> + switch (tlv[0]) {
> + case SND_CTL_TLVT_DB_RANGE: {
> + unsigned int pos, len;
> + len = tlv[1] / sizeof(int);
> + pos = 2;
>
> Be careful with this len limit in the while loop. I suggest adding a
> further comparison to limit the loop to a constant size:
> e.g.
> while (pos + 4 <= len && (pos + 4 < MAX_BUFFER_SIZE) ) {
> There are similar cases elsewhere in the patch.
Yes, it'd be safer. Will fix them.
>
> + while (pos + 4 <= len) {
> + rangemin = (int)tlv[pos];
> + rangemax = (int)tlv[pos + 1];
> + if (volume >= rangemin && volume <= rangemax)
> + return do_convert_to_dB(tlv + pos + 2,
> + rangemin, rangemax,
> + volume, db_gain);
> + pos += tlv[pos + 3] + 4;
> + }
> return -EINVAL;
>
>
> Apart from that, It looks OK to me.
>
> With regard to this control actually being to separate register in the
> chip, I think it might be nice to implement two separate controls
> between kernel and alsa-lib, but add some TLV tag to link the two
> controls together so that they appear as one. This will save code size
> in the kernel.
Agreed, this should really depend on the implementation.
In the case of es1938, however, it's clearly a single control (just
the dB scale curve is non-linear).
Thanks,
Takashi
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