[alsa-devel] question on dapm_reg_event()
Hi all,
I just have a question on dapm code. In dapm_reg_event(), -(w->reg + 1) is input parameter of snd_soc_update_bits(). Why we need to use negative value as input parameter at here? Why do we not use w->reg at here?
Thanks Haojian
On Mon, Jan 04, 2010 at 09:10:27PM -0500, Haojian Zhuang wrote:
I just have a question on dapm code. In dapm_reg_event(), -(w->reg +
- is input parameter of snd_soc_update_bits(). Why we need to use
negative value as input parameter at here? Why do we not use w->reg at here?
Hrm, no, that's not at all clear to me either. CCing Jarkko who contributed the register write control originally.
On Wed, 6 Jan 2010 14:53:22 +0000 Mark Brown broonie@opensource.wolfsonmicro.com wrote:
On Mon, Jan 04, 2010 at 09:10:27PM -0500, Haojian Zhuang wrote:
I just have a question on dapm code. In dapm_reg_event(), -(w->reg +
- is input parameter of snd_soc_update_bits(). Why we need to use
negative value as input parameter at here? Why do we not use w->reg at here?
Hrm, no, that's not at all clear to me either. CCing Jarkko who contributed the register write control originally.
IIRC, there were some reason to avoid register update by the dapm_update_bits and negative register value was used to prevent it.
Reg+1 makes sure that the value is negative also for register 0.
On Wed, Jan 06, 2010 at 05:48:59PM +0200, Jarkko Nikula wrote:
Mark Brown broonie@opensource.wolfsonmicro.com wrote:
Hrm, no, that's not at all clear to me either. CCing Jarkko who contributed the register write control originally.
IIRC, there were some reason to avoid register update by the dapm_update_bits and negative register value was used to prevent it.
Reg+1 makes sure that the value is negative also for register 0.
Ah, you're using some of the shared fields that the generic widget handling code then tries to interpret itself. It'd probably be less surprising to special case this widget in the generic code (as we do in a few other cases, like the PGA ramping).
participants (3)
-
Haojian Zhuang -
Jarkko Nikula -
Mark Brown