Re: [PATCH] ASoC: wm_hubs: Fix DC Servo readback

[Charles Keepax <ckeepax@opensource.wolfsonmicro.com>]

On Wed, Aug 13, 2014 at 01:16:37PM +0100, Charles Keepax wrote:
> On Wed, Aug 13, 2014 at 12:38:41PM +0100, Mark Brown wrote:
> > On Wed, Aug 13, 2014 at 12:08:44PM +0100, Charles Keepax wrote:
> > > On Wed, Aug 13, 2014 at 11:47:20AM +0100, Nikesh Oswal wrote:
> > 
> > > >  	case 2:
> > > >  		dcs_reg = WM8994_DC_SERVO_4E;
> > > >  		break;
> > > > -	case 1:
> > > > -		dcs_reg = WM8994_DC_SERVO_READBACK;
> > > > -		break;
> > > >  	default:
> > > >  		dcs_reg = WM8993_DC_SERVO_3;
> > > >  		break;
> > 
> > > This doesn't look right, firstly if it is the same register for
> > > all versions then surely we should change the code that sets
> > > dcs_readback_mode rather than setting that to different values
> > > but treating them the same. Although obviously if nothing still
> > > uses this case we could remove it as well.
> > 
> > > Also I think the situation is more complex for example on version
> > > 4.4 of the datasheet for wm8994 the WR_VAL fields appear to be in
> > > register 59h. Which is not consistent with this.
> > 
> > There was a change in the DC servo between revisions of the WM8994 (at
> > revision E from the look of the code).  This isn't documented in the
> > datasheets as they only document current silicon.
> 
> Indeed, but this patch sets all revs of wm8994 to use register 57h.
> The lastest version of the datasheet has this register at 59h
> although some of the older versions of the datasheet (which likely
> match some older revs of the chip although no way to tell which one
> just from the datasheet) have it at 57h.
> 
> I think basically we need to get some clarity from hardware here
> on which revs use which address and update this patch to match,
> but either way it looks likely that this patch doesn't address
> the whole picture.

Sorry no ignore me I am talking non-sense here. It still treats
the newer revs correctly, I suspect this might be a nice change
though:

--- a/sound/soc/codecs/wm_hubs.c
+++ b/sound/soc/codecs/wm_hubs.c
@@ -209,7 +209,7 @@ static int wm_hubs_read_dc_servo(struct
snd_soc_codec *codec,
                dcs_reg = WM8994_DC_SERVO_4E;
                break;
        case 1:
-               dcs_reg = WM8994_DC_SERVO_READBACK;
+               dcs_reg = WM8994_DC_SERVO_4;
                break;

Thanks,
Charles