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

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Message-ID: <048dd9a2d3257ddea4e4223b023bde9747469083.camel@apitzsch.eu>
Date: Thu, 18 Sep 2025 23:31:18 +0200
From: André Apitzsch <git@...tzsch.eu>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>, Val Packett
 <val@...kett.cool>
Cc: 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 Sakari,

Am Mittwoch, dem 17.09.2025 um 13:10 +0300 schrieb Sakari Ailus:
> 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?

Could you clarify which information.

Best regards,
André