linux-kernel - Re: [PATCH 7/7] media: i2c: dw9719: Fix power on/off sequence

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Message-ID: <aMqI-lElZsWV-Hrl@kekkonen.localdomain>
Date: Wed, 17 Sep 2025 13:10:02 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Val Packett <val@...kett.cool>
Cc: André Apitzsch <git@...tzsch.eu>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
	Daniel Scally <djrscally@...il.com>,
	~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] media: i2c: dw9719: Fix power on/off sequence

Hi André, Val,

On Tue, Sep 16, 2025 at 05:08:44PM -0300, Val Packett wrote:
> 
> On 9/15/25 5:48 PM, André Apitzsch wrote:
> > Hi Sakari,
> > 
> > @Val, please see below.
> > 
> > Am Montag, dem 18.08.2025 um 07:44 +0000 schrieb Sakari Ailus:
> > > Hi André,
> > > 
> > > On Sun, Aug 17, 2025 at 07:09:26PM +0200, André Apitzsch via B4 Relay
> > > wrote:
> > > >   	u64 val;
> > > >   	int ret;
> > > >   	int err;
> > > > @@ -109,13 +116,15 @@ static int dw9719_power_up(struct
> > > > dw9719_device *dw9719, bool detect)
> > > >   	if (ret)
> > > >   		return ret;
> > > > -	/* Jiggle SCL pin to wake up device */
> > > > -	reg_pwr = (dw9719->model == DW9718S) ? DW9718S_PD :
> > > > DW9719_CONTROL;
> > > > -	cci_write(dw9719->regmap, reg_pwr, DW9719_SHUTDOWN, &ret);
> > > > -	fsleep(100);
> > > > +	/*
> > > > +	 * Need 100us to transition from SHUTDOWN to STANDBY.
> > > > +	 * Jiggle the SCL pin to wake up the device (even when the
> > > > regulator
> > > > +	 * is shared) and wait double the time to be sure, then
> > > > retry the write.
> > > Why double? Isn't the datasheet correct when it comes to the power-on
> > > sequence?
> > > 
> > I haven't noticed any problems during power-up of DW9761. However,
> > according to the commit message, there seems be an issue with DW9718S.
> > But I don't own the device and cannot test it.
> > 
> > Maybe Val can provided some additional information.
> 
> I haven't had access to the datasheet for the DW9718S, so this was all
> deduced experimentally. By "to be sure" I meant that I literally raised the
> timeout "just in case", not based on actual issues.
> 
> The actually important change was expecting the failure on the write and not
> erroring out.

Ack.

André: could you add this information to the comment as well?

-- 
Kind regards,

Sakari Ailus