Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux

[Lars-Peter Clausen]

On 03/29/2014 03:30 AM, Songhee Baek wrote:
> > -----Original Message-----
> > From: Songhee Baek
> > Sent: Friday, March 28, 2014 11:10 AM
> > To: 'Lars-Peter Clausen'
> > Cc: Arun Shamanna Lakshmi; 'lgirdwood@xxxxxxxxx'; 'broonie@xxxxxxxxxx';
> > 'swarren@xxxxxxxxxxxxx'; 'alsa-devel@xxxxxxxxxxxxxxxx'; 'tiwai@xxxxxxx';
> > 'linux-kernel@xxxxxxxxxxxxxxx'
> > Subject: RE: [alsa-devel] [PATCH] ASoC: Add support for multi register mux
> >
> >
> > > > On 03/26/2014 11:41 PM, Songhee Baek wrote:
> > > > > > On 03/26/2014 01:02 AM, Arun Shamanna Lakshmi wrote:
> > > > > >
> > > > > > The way you describe this it seems to me that a value array for
> > > > > > this kind of mux would look like.
> > > > > >
> > > > > > 0x00000000, 0x00000000, 0x00000001 0x00000000, 0x00000000,
> > > > > > 0x00000002 0x00000000, 0x00000000, 0x00000003 0x00000000,
> > > > > > 0x00000000, 0x00000004 0x00000000, 0x00000000, 0x00000008 ...
> > > > > >
> > > > > > That seems to be extremely tedious. If the MUX uses a one hot
> > > > > > encoding how about storing the index of the bit in the values
> > > > > > array and use (1 << value) when writing the value to the register?
> > > > >
> > > > > If we store the index of the bit, the value will be duplicated for
> > > > > each
> > > > registers inputs since register has 0 to 31bits to shift, then we
> > > > need to decode the index to interpret value for which registers to
> > > > set. If we need to interpret the decoded value of index, it is
> > > > better to have custom put/get function in our driver, isn't it?
> > > > >
> > > >
> > > > I'm not sure I understand. If you use (val / 32) to pick the
> > > > register and (val %
> > > > 32) to pick the bit in the register this should work just fine.
> > > > Maybe I'm missing something. Do you have a real world code example
> > > > of of the this type of enum is used?
> > >
> > > I can use val/32 and val%32 for this multi register mux.
> With this logic, put function would be easy however get function becomes tedious due to looping on each bit per register for 3 of them in our case. Rather, it would be easy to identify a unique MUX_OFFSET to distinguish between the 3
> registers as shown in the code below.

I'm not sure I understand how that MUX_OFFSET would work. To get the 
selected mux output you can use the ffs instruction.

foreach(reg) {
	reg_val = read(reg) & mask;
	if (reg_val != 0) {
		val = __ffs(reg_val);
		break;
	}
}

- Lars
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/