Re: [PATCH v4 2/2] media: i2c: Add GC08A3 image sensor driver

["Zhi Mao (毛智)" <zhi.mao@mediatek.com>]

Hi Laurent & sakari,

Thanks for your feedback.

On Tue, 2024-02-20 at 07:25 +0000, sakari.ailus@linux.intel.com wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  Hi Zhi,
> 
> On Tue, Feb 20, 2024 at 05:45:54AM +0000, Zhi Mao (毛智) wrote:
> > Hi Laurent,
> > 
> > Thanks for you reply.
> > I'd like to ask for advice about how to contrl "reset-pin", please
> > check the below comments.
> > 
> > On Tue, 2024-02-20 at 05:01 +0200, Laurent Pinchart wrote:
> > >   
> > > External email : Please do not click links or open attachments
> until
> > > you have verified the sender or the content.
> > >  Hi Zhi,
> > > 
> > > On Tue, Feb 20, 2024 at 02:12:26AM +0000, Zhi Mao (毛智) wrote:
> > > > On Tue, 2024-02-06 at 20:45 +0200, Laurent Pinchart wrote:
> > > > > On Sun, Feb 04, 2024 at 02:15:38PM +0800, Zhi Mao wrote:
> > > > > > Add a V4L2 sub-device driver for Galaxycore GC08A3 image
> > > sensor.
> > > > > >
> > > > > > Signed-off-by: Zhi Mao <zhi.mao@mediatek.com>
> > > > > > ---
> > > > > >  drivers/media/i2c/Kconfig  |   10 +
> > > > > >  drivers/media/i2c/Makefile |    1 +
> > > > > >  drivers/media/i2c/gc08a3.c | 1448
> > > ++++++++++++++++++++++++++++++++++++
> > > > > >  3 files changed, 1459 insertions(+)
> > > > > >  create mode 100644 drivers/media/i2c/gc08a3.c
> > > 
> > > [snip]
> > > 
> > > > > > diff --git a/drivers/media/i2c/gc08a3.c
> > > b/drivers/media/i2c/gc08a3.c
> > > > > > new file mode 100644
> > > > > > index 000000000000..3fc7fffb815c
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/media/i2c/gc08a3.c
> > > > > > @@ -0,0 +1,1448 @@
> > > 
> > > [snip]
> > > 
> > > > > > +static int gc08a3_power_on(struct device *dev)
> > > > > > +{
> > > > > > +struct i2c_client *client = to_i2c_client(dev);
> > > > > > +struct v4l2_subdev *sd = i2c_get_clientdata(client);
> > > > > > +struct gc08a3 *gc08a3 = to_gc08a3(sd);
> > > > > > +int ret;
> > > > > > +
> > > > > > +ret =
> regulator_bulk_enable(ARRAY_SIZE(gc08a3_supply_name),
> > > > > > +    gc08a3->supplies);
> > > > > > +if (ret < 0) {
> > > > > > +dev_err(gc08a3->dev, "failed to enable regulators: %d\n",
> > > ret);
> > > > > > +return ret;
> > > > > > +}
> > > > > > +
> > > > > > +ret = clk_prepare_enable(gc08a3->xclk);
> > > > > > +if (ret < 0) {
> > > > > > +regulator_bulk_disable(ARRAY_SIZE(gc08a3_supply_name),
> > > > > > +       gc08a3->supplies);
> > > > > > +dev_err(gc08a3->dev, "clk prepare enable failed\n");
> > > > > > +return ret;
> > > > > > +}
> > > > > > +
> > > > > > +usleep_range(GC08A3_MIN_SLEEP_US, GC08A3_MAX_SLEEP_US);
> > > > > > +
> > > > > > +gpiod_set_value_cansleep(gc08a3->reset_gpio, 1);
> > > > >
> > > > > Are you asserting reset when powering on ? That sounds wrong,
> you
> > > should
> > > > > de-assert reset here (and acquire the reset gpio in probe()
> with
> > > > > GPIOD_OUT_HIGH). Drivers should use logical levels for GPIOs,
> > > setting a
> > > > > GPIO named "reset" to 1 should assert the reset signal, even
> if
> > > the
> > > > > physical signal is active low. You may have the wrong
> polarity in
> > > the
> > > > > device tree.
> > > >
> > > > According to the sensor power sequence sepc, "reset" pin should
> be
> > > pull
> > > > from low to high after "dovdd/dvdd/avdd" power on, so I follow
> this
> > > > power sequece to pull "reset" pin high in software flow.
> > > 
> > > From a hardware point of view that's right, but the Linux kernel
> > > handles
> > > logical level of GPIOs. If a GPIO is named "reset", it is
> expected
> > > that
> > > calling
> > > 
> > > gpiod_set_value_cansleep(gc08a3->reset_gpio, 1);
> > > 
> > > will "assert" the reset signal, setting it to a logical "reset =
> > > true"
> > > level. This maps to the hardware 0V output level, as the signal
> is
> > > active-low. To achieve this, define the reset GPIO as active low
> in
> > > DT,
> > > and the GPIO framework will invert the signal for you. You should
> > > then
> > > call
> > > 
> > > gpiod_set_value_cansleep(gc08a3->reset_gpio, 1);
> > > 
> > > in the driver when you want to assert reset (set it to 0V), and
> > > 
> > > gpiod_set_value_cansleep(gc08a3->reset_gpio, 0);
> > > 
> > > when you want to deassert it (set it to 3.3V, or whatever the I/O
> > > voltage for the signal is).
> > > 
> > > This way all driver use logical states, and the inversion is
> handled
> > > in
> > > DT.
> > > 
> > 
> > Sensor power sequence as below:
> >                       ------------------
> >                      | | |
> >                      | | | 
> > dvdd/avdd/dovdd  --------
> >                                ---------
> >                               |
> >                               |
> > reset-pin        -------------
> > 
> > In order to match this power sequece, "reset-pin" contrl flow is
> below:
> > 1. config the "reset-pin" is "active-high" in DTS:
> >     reset-gpios = <&pio 19 GPIO_ACTIVE_HIGH>;
> > 
> > 2. image sensor driver probe function:
> > gc08a3->reset_gpio = devm_gpiod_get(dev, "reset",
> > GPIOD_OUT_LOW);  //init "reset-pin" is low
> > 
> > 3. image sensor driver power_on function:
> > gpiod_set_value_cansleep(gc08a3->reset_gpio, 1); //pull "reset-pin"
> > high 
> > 
> > so, the expect state of "reset-pin" is from low to high.
> > If I am wrong, please correct me.
> 
> 
> From Documentation/driver-api/gpio/consumer.rst:
> 
> As a consumer should not have to care about the physical line
> level, all of the gpiod_set_value_xxx() or
> gpiod_set_array_value_xxx() functions operate with the *logical*
> value. With this they take the active low property into account.
> This means that they check whether the GPIO is configured to be
> active low, and if so, they manipulate the passed value before the
> physical line level is driven.
> 
> I.e. when you want to enable reset, you set the value to 1 in the
> driver. I
> think you're now setting the value to 0 in that case. The opposite
> for
> disabling it of course.
> 
After checking "Documentation/driver-api/gpio/consumer.rst":
To summarize::
  Function (example)                 line property          physical
line
...
  gpiod_set_value(desc, 1);          default (active high)  high
  gpiod_set_value(desc, 0);          active low             high
...


From my understanding, it seems that "reset-pin" is using the
following(active_high) case in current code: 
"gpiod_set_value(desc, 1);          default (active high)  high" 

Do you mean, we should use the "active_low" case:
"gpiod_set_value(desc, 0);          active low             high"
Code should be changed as below:
1. config the "reset-pin" is "active-low" in DTS:
   - reset-gpios = <&pio 19 GPIO_ACTIVE_LOW>
2. image sensor driver power_on function:
   - gpiod_set_value_cansleep(gc08a3->reset_gpio, 0); //pull high 
Is that so?


> -- 
> Regards,
> 
> Sakari Ailus