Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Wed, 1 Jun 2022 10:11:29 +0200
From:   Jacopo Mondi <jacopo@jmondi.org>
To:     Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
Cc:     Tommaso Merciai <tommaso.merciai@amarulasolutions.com>,
        linuxfancy@googlegroups.com, linux-amarula@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
Message-ID: <20220601081129.jlasfmvjyvqr4brd@uno.localdomain>
References: <20220519075117.1003520-1-tommaso.merciai@amarulasolutions.com>
 <20220519075117.1003520-2-tommaso.merciai@amarulasolutions.com>
 <20220531131409.f54znvogejkwqqkf@uno.localdomain>
 <20220531154040.GA1331064@tom-ThinkPad-T14s-Gen-2i>
 <CAOf5uwmNoSPifCo8_hLZyr=DzMqL0r2Ftot2jneEVpAT8AyYVg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAOf5uwmNoSPifCo8_hLZyr=DzMqL0r2Ftot2jneEVpAT8AyYVg@mail.gmail.com>
Precedence: bulk

Hi Micheal,

On Tue, May 31, 2022 at 05:50:51PM +0200, Michael Nazzareno Trimarchi wrote:
> Hi
>
> On Tue, May 31, 2022 at 5:40 PM Tommaso Merciai
> <tommaso.merciai@amarulasolutions.com> wrote:
> >
> > 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
> > >
>
> They are enabled on the array 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.
>
> I don't think so. Will make no sense because if it fails, revert them.
> Even the bulk disable disable them
> in reverse order
>

I understand your points, but even the commit message in the patch
linked by Tommaso [1] (which I see in mainline as
f1a64f56663e ("media: i2c: ov5695: Fix power on and off sequences"))
reports:

"Given the bulk API does not give any guarantee about the order of
regulators, change the driver to use regulator_disable() instead."

However I would have expected the core regulator API to clearly document
this behaviour.


> > >
> > > 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]
> >
>
> WHy drop?

As this is a partial revert of [1].

I think in practice this won't make any actual difference, but if not
100% sure, better leave it the way it is as the authors of [1] might
have actually been experiencing issues. Even more as this patch is
not a bugfix but a nice-to-have. Up to you :)


>
> Michael
>
> > >
> > > > +   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
> > __________________________________
> >
> > Amarula Solutions SRL
> > Via Le Canevare 30, 31100 Treviso, Veneto, IT
> > T. +39 042 243 5310
> > info@amarulasolutions.com
> > www.amarulasolutions.com
>
>
>
> --
> Michael Nazzareno Trimarchi
> Co-Founder & Chief Executive Officer
> M. +39 347 913 2170
> michael@amarulasolutions.com
> __________________________________
>
> Amarula Solutions BV
> Joop Geesinkweg 125, 1114 AB, Amsterdam, NL
> T. +31 (0)85 111 9172
> info@amarulasolutions.com
> www.amarulasolutions.com