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

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Date:   Wed, 9 Mar 2022 16:19:31 +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 03:56:12PM +0000, Mark Brown wrote:
> On Wed, Mar 09, 2022 at 01:56:49PM +0000, John Keeping wrote:
> 
> > The binding defines the GPIO as "pdn-gpios" so when the GPIO is active
> > the expectation is that the power down signal is asserted and this is
> > how all other drivers using this GPIO name interpret the value.
> 
> > But the tas5805m driver inverts the sense from the normal expectation so
> > when the powerdown GPIO is logically asserted the chip is running.
> 
> > This is a new driver that is not yet in a released kernel and has no
> > in-tree users of the binding so fix the sense of the GPIO so that
> > logically asserted means that the device is powered down.
> 
> > - Rewrite commit message to make it more obvious that this is a change
> >   to the interpretation of the GPIO in the binding
> 
> 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.