linux-kernel - Re: [PATCH v2] regulator: wm8994: Add an off-on delay for WM8994 variant

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Message-ID: <20220328131132.GI38351@ediswmail.ad.cirrus.com>
Date:   Mon, 28 Mar 2022 13:11:32 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Jonathan Bakker <xc-racer2@...e.ca>
CC:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] regulator: wm8994: Add an off-on delay for WM8994
 variant

On Sun, Mar 27, 2022 at 06:01:54PM -0700, Jonathan Bakker wrote:
> As per Table 130 of the wm8994 datasheet at [1], there is an off-on
> delay for LDO1 and LDO2.  In the wm8958 datasheet [2], I could not
> find any reference to it.  I could not find a wm1811 datasheet to
> double-check there, but as no one has complained presumably it works
> without it.
> 
> This solves the issue on Samsung Aries boards with a wm8994 where
> register writes fail when the device is powered off and back-on
> quickly.
> 
> [1] https://statics.cirrus.com/pubs/proDatasheet/WM8994_Rev4.6.pdf
> [2] https://statics.cirrus.com/pubs/proDatasheet/WM8958_v3.5.pdf
> 
> Signed-off-by: Jonathan Bakker <xc-racer2@...e.ca>
> ---

I can confirm the 1811 also doesn't mention the cycle time in the
datasheet. So that checks out.

Acked-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Part of me wonders if we should just apply it to 1811 and 8958
anyway, I suspect they have the same IP for the LDO and its just
the datasheets never got updated. I had a go chasing the apps guys
here but we are a little short on people who remember details of
these parts. So I guess we trust the datasheets for now, unless
you have any strong feelings, Mark?

Thanks,
Charles