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Message-ID: <20220711162533.fycvqnaffk4tdfda@uno.localdomain>
Date: Mon, 11 Jul 2022 18:25:33 +0200
From: Jacopo Mondi <jacopo@...ndi.org>
To: Yassine Oudjana <yassine.oudjana@...il.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Tianshu Qiu <tian.shu.qiu@...el.com>,
Bingbu Cao <bingbu.cao@...el.com>,
Yassine Oudjana <y.oudjana@...tonmail.com>,
linux-media@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] media: i2c: ak7375: Add regulator management
Hi Yassine
On Mon, Jul 11, 2022 at 06:08:53PM +0400, Yassine Oudjana wrote:
>
> On Mon, Jul 11 2022 at 15:34:23 +0200, Jacopo Mondi <jacopo@...ndi.org>
> wrote:
> > Hello Yassine
> >
> > On Mon, Jul 11, 2022 at 08:28:39AM +0400, Yassine Oudjana wrote:
> > > From: Yassine Oudjana <y.oudjana@...tonmail.com>
> > >
> > > Make the driver get needed regulators on probe and enable/disable
> > > them on runtime PM callbacks.
> > >
> > > Signed-off-by: Yassine Oudjana <y.oudjana@...tonmail.com>
> > > ---
> > > drivers/media/i2c/ak7375.c | 39
> > > ++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 39 insertions(+)
> > >
> > > diff --git a/drivers/media/i2c/ak7375.c b/drivers/media/i2c/ak7375.c
> > > index 40b1a4aa846c..59d5cb00e3ba 100644
> > > --- a/drivers/media/i2c/ak7375.c
> > > +++ b/drivers/media/i2c/ak7375.c
> > > @@ -6,6 +6,7 @@
> > > #include <linux/i2c.h>
> > > #include <linux/module.h>
> > > #include <linux/pm_runtime.h>
> > > +#include <linux/regulator/consumer.h>
> > > #include <media/v4l2-ctrls.h>
> > > #include <media/v4l2-device.h>
> > >
> > > @@ -23,17 +24,32 @@
> > > */
> > > #define AK7375_CTRL_STEPS 64
> > > #define AK7375_CTRL_DELAY_US 1000
> > > +/*
> > > + * The vcm takes around 3 ms to power on and start taking
> > > + * I2C messages. This value was found experimentally due to
> > > + * lack of documentation. 2 ms is added as a safety margin.
> > > + */
> > > +#define AK7375_POWER_DELAY_US 5000
> > >
> > > #define AK7375_REG_POSITION 0x0
> > > #define AK7375_REG_CONT 0x2
> > > #define AK7375_MODE_ACTIVE 0x0
> > > #define AK7375_MODE_STANDBY 0x40
> > >
> > > +static const char * const ak7375_supply_names[] = {
> > > + "vdd",
> > > + "vio",
> > > +};
> > > +
> > > +#define AK7375_NUM_SUPPLIES ARRAY_SIZE(ak7375_supply_names)
> > > +
> > > /* ak7375 device structure */
> > > struct ak7375_device {
> > > struct v4l2_ctrl_handler ctrls_vcm;
> > > struct v4l2_subdev sd;
> > > struct v4l2_ctrl *focus;
> > > + struct regulator_bulk_data supplies[AK7375_NUM_SUPPLIES];
> > > +
> > > /* active or standby mode */
> > > bool active;
> > > };
> > > @@ -132,6 +148,7 @@ static int ak7375_init_controls(struct
> > > ak7375_device *dev_vcm)
> > > static int ak7375_probe(struct i2c_client *client)
> > > {
> > > struct ak7375_device *ak7375_dev;
> > > + int i;
> >
> > I would have moved this one down to maintain variable declaration
> > in the in-famous reverse-xmas-tree ordering. Up to you.
>
> I'm used to declaring variables in the order of first use,
> but I don't really mind it either way. I'll move it down.
>
> >
> > > int ret;
> > >
> > > ak7375_dev = devm_kzalloc(&client->dev, sizeof(*ak7375_dev),
> > > @@ -139,6 +156,17 @@ static int ak7375_probe(struct i2c_client
> > > *client)
> > > if (!ak7375_dev)
> > > return -ENOMEM;
> > >
> > > + for (i = 0; i < AK7375_NUM_SUPPLIES; i++)
> > > + ak7375_dev->supplies[i].supply = ak7375_supply_names[i];
> > > +
> > > + ret = devm_regulator_bulk_get(&client->dev, AK7375_NUM_SUPPLIES,
> > > + ak7375_dev->supplies);
> > > + if (ret) {
> > > + dev_err(&client->dev, "Failed to get regulators: %pe",
> > > + ERR_PTR(ret));
> > > + return ret;
> > > + }
> > > +
> > > v4l2_i2c_subdev_init(&ak7375_dev->sd, client, &ak7375_ops);
> > > ak7375_dev->sd.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> > > ak7375_dev->sd.internal_ops = &ak7375_int_ops;
> > > @@ -210,6 +238,10 @@ static int __maybe_unused
> > > ak7375_vcm_suspend(struct device *dev)
> > > if (ret)
> > > dev_err(dev, "%s I2C failure: %d\n", __func__, ret);
> > >
> > > + ret = regulator_bulk_disable(AK7375_NUM_SUPPLIES,
> > > ak7375_dev->supplies);
> > > + if (ret)
> > > + return ret;
> > > +
> > > ak7375_dev->active = false;
> > >
> > > return 0;
> > > @@ -230,6 +262,13 @@ static int __maybe_unused
> > > ak7375_vcm_resume(struct device *dev)
> > > if (ak7375_dev->active)
> > > return 0;
> > >
> > > + ret = regulator_bulk_enable(AK7375_NUM_SUPPLIES,
> > > ak7375_dev->supplies);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + /* Wait for vcm to become ready */
> > > + usleep_range(AK7375_POWER_DELAY_US, AK7375_POWER_DELAY_US + 10);
> > > +
> >
> > Isn't 10usec a very small delay to be given to usleep_range() for a
> > delay of at least 3msec ? Also assuming 5msec just to be safe seems a
> > little arbitrary. Adding 2 milliseconds in the wakeup path introduces
> > a non-negligible delay.
>
> I must admit that I didn't give it too much thought. I just
> did it similar to the other delay used in this driver
> (AK7375_CTRL_DELAY_US). As for adding 2ms, I don't know what
> the worst case wake-up time is since I don't have a datasheet
> on hand, so I just wanted to stay safe. Also, this driver
Oh sorry, I missed in the comment the value was found experimentally
an it's not documented..
> doesn't really recover if it fails to resume (which is what
> used to happen before adding a delay). Rounding up to 5ms
> felt good enough.
>
> >
> > It's likely a detail, but according to
> > Documentation/timers/timers-howto.rst
> >
> > Since usleep_range is built on top of hrtimers, the
> > wakeup will be very precise (ish), thus a simple
> > usleep function would likely introduce a large number
> > of undesired interrupts.
> >
> > With the introduction of a range, the scheduler is
> > free to coalesce your wakeup with any other wakeup
> > that may have happened for other reasons, or at the
> > worst case, fire an interrupt for your upper bound.
> >
> > The larger a range you supply, the greater a chance
> > that you will not trigger an interrupt; this should
> > be balanced with what is an acceptable upper bound on
> > delay / performance for your specific code path. Exact
> > tolerances here are very situation specific, thus it
> > is left to the caller to determine a reasonable range.
> >
> > If you have a min of 3msec I would try with a range of (3000, 3500).
> > What do you think ?
>
> Seems good. I haven't yet had it fail to power on within 3ms of
> turning on regulators so I guess there is no reason to worry about it.
>
Ok then :) There's anyway a comment that says the value comes from
practical experience, so if anything bad happens, it's easy to track
it down to that
Thanks
j
> > >
> > > ret = ak7375_i2c_write(ak7375_dev, AK7375_REG_CONT,
> > > AK7375_MODE_ACTIVE, 1);
> > > if (ret) {
> > > --
> > > 2.37.0
> >
>
> Thanks for the review,
> Yassine
>
>
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