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

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Message-ID: <550f28a9aa82a28beb35fd3490dbe08928ba9eed.camel@apitzsch.eu>
Date: Mon, 15 Sep 2025 22:48:23 +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,

@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:
> > From: Val Packett <val@...kett.cool>
> > 
> > The "jiggle" code was not actually expecting failure, which it
> > should because that's what actually happens when the device wasn't
> > already woken up by the regulator power-on (i.e. in the case of a
> > shared regulator).
> > 
> > Also, do actually enter the internal suspend mode on shutdown, to
> > save power in the case of a shared regulator.
> > 
> > Also, wait a bit longer (2x tOPR) on waking up, 1x is not enough at
> > least on the DW9718S as found on the motorola-nora smartphone.
> > 
> > Signed-off-by: Val Packett <val@...kett.cool>
> > Signed-off-by: André Apitzsch <git@...tzsch.eu>
> > ---
> >  drivers/media/i2c/dw9719.c | 23 ++++++++++++++++-------
> >  1 file changed, 16 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/dw9719.c
> > b/drivers/media/i2c/dw9719.c
> > index
> > 63c7fd4ab70a0e02518252b23b89c45df4ba273d..dd28a0223d6ac980084b1f661
> > bd029ea6b0be503 100644
> > --- a/drivers/media/i2c/dw9719.c
> > +++ b/drivers/media/i2c/dw9719.c
> > @@ -95,12 +95,19 @@ struct dw9719_device {
> >  
> >  static int dw9719_power_down(struct dw9719_device *dw9719)
> >  {
> > +	u32 reg_pwr = (dw9719->model == DW9718S) ? DW9718S_PD :
> > DW9719_CONTROL;
> 
> Extra parentheses.
> 
> > +
> > +	/*
> > +	 * Worth engaging the internal SHUTDOWN mode especially
> > due to the
> > +	 * regulator being potentially shared with other devices.
> > +	 */
> > +	cci_write(dw9719->regmap, reg_pwr, DW9719_SHUTDOWN, NULL);
> 
> I'd still complain if this fails as we don't return the error.
> 
> >  	return regulator_disable(dw9719->regulator);
> >  }
> >  
> >  static int dw9719_power_up(struct dw9719_device *dw9719, bool
> > detect)
> >  {
> > -	u32 reg_pwr;
> > +	u32 reg_pwr = (dw9719->model == DW9718S) ? DW9718S_PD :
> > DW9719_CONTROL;
> 
> Extra parentheses.
> 
> >  	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.

Best regards,
André

> > +	 */
> > +	cci_write(dw9719->regmap, reg_pwr, DW9719_STANDBY, &ret);
> > +	ret = 0; /* the jiggle is expected to fail, don't even log
> > that as error */
> > +	fsleep(200);
> >  	cci_write(dw9719->regmap, reg_pwr, DW9719_STANDBY, &ret);
> 
> Just pass NULL instead of ret as we don't check the value and the ret
> assignment above becomes redundant. Please spare the comment though.
> 
> > -	/* Need 100us to transit from SHUTDOWN to STANDBY */
> > -	fsleep(100);
> >  
> >  	if (detect) {
> >  		/* This model does not have an INFO register */
> >