Re: [PATCH 1/4] media: i2c: ov5695: use regulator_bulk_enable/regulator_bulk disable instead of for loop

From: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
To: Jacopo Mondi <jacopo@jmondi.org>
Cc: linuxfancy@googlegroups.com, linux-amarula@amarulasolutions.com,
	michael@amarulasolutions.com,
	Shunqian Zheng <zhengsq@rock-chips.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] media: i2c: ov5695: use regulator_bulk_enable/regulator_bulk disable instead of for loop
Date: Tue, 31 May 2022 17:40:40 +0200	[thread overview]
Message-ID: <20220531154040.GA1331064@tom-ThinkPad-T14s-Gen-2i> (raw)
In-Reply-To: <20220531131409.f54znvogejkwqqkf@uno.localdomain>

Hi Jacopo,
On Tue, May 31, 2022 at 03:14:09PM +0200, Jacopo Mondi wrote:
> Hi Tommaso,
> 
> On Thu, May 19, 2022 at 09:51:14AM +0200, Tommaso Merciai wrote:
> > Enable regulator using regulator_bulk_enable/regulatore_bulk_disable
> > function in __ov5695_power_on/__ov5695_power_off function instead of for loop.
> > This reduce code size and make things more clear
> >
> > Signed-off-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
> > Co-Developed-by: Michael Trimarchi <michael@amarulasolutions.com>
> > ---
> >  drivers/media/i2c/ov5695.c | 25 +++++++------------------
> >  1 file changed, 7 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/media/i2c/ov5695.c b/drivers/media/i2c/ov5695.c
> > index 439385938a51..880b586e55fe 100644
> > --- a/drivers/media/i2c/ov5695.c
> > +++ b/drivers/media/i2c/ov5695.c
> > @@ -972,7 +972,7 @@ static int ov5695_s_stream(struct v4l2_subdev *sd, int on)
> >
> >  static int __ov5695_power_on(struct ov5695 *ov5695)
> >  {
> > -	int i, ret;
> > +	int ret;
> >  	struct device *dev = &ov5695->client->dev;
> >
> >  	ret = clk_prepare_enable(ov5695->xvclk);
> > @@ -987,13 +987,10 @@ static int __ov5695_power_on(struct ov5695 *ov5695)
> >  	 * The hardware requires the regulators to be powered on in order,
> >  	 * so enable them one by one.
> >  	 */
> 
> The comment says that the hardware requires regulators to be enabled
> in precise order
> 
> > -	for (i = 0; i < OV5695_NUM_SUPPLIES; i++) {
> > -		ret = regulator_enable(ov5695->supplies[i].consumer);
> > -		if (ret) {
> > -			dev_err(dev, "Failed to enable %s: %d\n",
> > -				ov5695->supplies[i].supply, ret);
> > -			goto disable_reg_clk;
> > -		}
> > +	ret = regulator_bulk_enable(ARRAY_SIZE(ov5695->supplies), ov5695->supplies);
> 
> bulk_enable() uses the async API (async_schedule_domain() in
> particular) which by the name makes me think such ordering guarantee
> cannot be respected.
> 
> However most sensors require some kind of ordering when enabling
> regulators, and most of the use the bulk API anyhow. The fact this
> driver uses the bulk API to get an release the regulators but not for
> enabling them and the above comment, makes me think it has been done
> on purpose ? Could you check with the driver author maybe ?

Thanks for suggestion, good question.
I see also ov5693 driver use bulk_enable/bulk_disable
on ov5693_sensor_powerdown and ov5693_sensor_powerup functions, I take
this as reference (and I'm wrong)

In a functional test on PX30_Mini_evb_v11_20190507, after this series 
I'm able to see the correct chip id during probe and do some capture.

I think you are right Jacopo, we can drop off this [PATCH 1/4]
On the following link I found the issue that you describe: [1]

> 
> > +	if (ret) {
> > +		dev_err(dev, "Failed to enable regulators %d\n", ret);
> > +		goto disable_reg_clk;
> >  	}
> >
> >  	gpiod_set_value_cansleep(ov5695->reset_gpio, 0);
> > @@ -1003,8 +1000,7 @@ static int __ov5695_power_on(struct ov5695 *ov5695)
> >  	return 0;
> >
> >  disable_reg_clk:
> > -	for (--i; i >= 0; i--)
> > -		regulator_disable(ov5695->supplies[i].consumer);
> > +	regulator_bulk_disable(ARRAY_SIZE(ov5695->supplies), ov5695->supplies);
> 
> FYI the bulk API does this for you if enabling any of the regulators fails.
> Hence this should not be necessary.

Thanks for sharing! This is new to me.
I'll update the series on v2 removing this patch.

Regards,
Tommaso

[1]: https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/4X54QYJDRRE4K5BW4FTDZUGRAL4GRQWY/

> Thanks
>    j
> 
> >  	clk_disable_unprepare(ov5695->xvclk);
> >
> >  	return ret;
> > @@ -1012,8 +1008,6 @@ static int __ov5695_power_on(struct ov5695 *ov5695)
> >
> >  static void __ov5695_power_off(struct ov5695 *ov5695)
> >  {
> > -	struct device *dev = &ov5695->client->dev;
> > -	int i, ret;
> >
> >  	clk_disable_unprepare(ov5695->xvclk);
> >  	gpiod_set_value_cansleep(ov5695->reset_gpio, 1);
> > @@ -1022,12 +1016,7 @@ static void __ov5695_power_off(struct ov5695 *ov5695)
> >  	 * The hardware requires the regulators to be powered off in order,
> >  	 * so disable them one by one.
> >  	 */
> > -	for (i = OV5695_NUM_SUPPLIES - 1; i >= 0; i--) {
> > -		ret = regulator_disable(ov5695->supplies[i].consumer);
> > -		if (ret)
> > -			dev_err(dev, "Failed to disable %s: %d\n",
> > -				ov5695->supplies[i].supply, ret);
> > -	}
> > +	regulator_bulk_disable(ARRAY_SIZE(ov5695->supplies), ov5695->supplies);
> >  }
> >
> >  static int __maybe_unused ov5695_runtime_resume(struct device *dev)
> > --
> > 2.25.1
> >

-- 
Tommaso Merciai
Embedded Linux Engineer
tommaso.merciai@amarulasolutions.com
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