linux-kernel - Re: [PATCH v2] ASoC: tas5805m: fix pdn polarity

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Date:   Wed, 9 Mar 2022 20:16:07 +0000
From:   John Keeping <john@...anate.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     alsa-devel@...a-project.org, Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Daniel Beer <daniel.beer@...rinstitute.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ASoC: tas5805m: fix pdn polarity

On Wed, Mar 09, 2022 at 04:28:30PM +0000, Mark Brown wrote:
> On Wed, Mar 09, 2022 at 04:19:31PM +0000, John Keeping wrote:
> > On Wed, Mar 09, 2022 at 03:56:12PM +0000, Mark Brown wrote:
> 
> > > I'm still not seeing the functional change here.  The actual state of
> > > the GPIO is identical in both cases, all that's changing is the logical
> > > view internally to the kernel.
> 
> > Ah, sorry, I'm considering it functional since it changes the device
> > tree ABI.
> 
> > Used with the same device tree with, say, GPIO_ACTIVE_HIGH the physical
> > state of the GPIO will change as a result of this patch and the device
> > tree needs to be updated to use GPIO_ACTIVE_LOW.
> 
> I think the device tree binding needs to be clarified here to be
> explicit about this since there's obviously some room for user confusion
> here.  We can probably get away with a change at this point since it's
> not hit a release but we do need to try to avoid the situation where any
> other implementations use active high polarity for the bindings.

Taking a quick survey of the other devices that have a pdn-gpios
property:

- tvp5150 is correct with the driver setting 0 to make the device active

- tas571x also sets 0 to make the device active

- ak4375 uses the opposite sense setting PDN = 1 to make the device
  active; this has no in-tree users and was merged as part of v5.17-rc1
  so it's not in a released kernel yet