Re: [PATCH v7 2/5] media: i2c: imx355: Support devicetree and power management

[Richard Acayan <mailingradian@gmail.com>]

On Tue, Jan 20, 2026 at 04:49:21PM +0200, Sakari Ailus wrote:
> Hi Bryan, others,
> 
> On Tue, Jan 20, 2026 at 12:44:24PM +0000, Bryan O'Donoghue wrote:
> > I think reset should be asserted before regulators and power are switched
> > on. i.e. before you try to switch the chip on, you should establish that the
> > reset pin is in the state that the timing diagram calls for.
> 
> Indeed.

I think the discussion is more about whether there should be an assert
in the same function as the de-assert.

> The xshutdown pin, as it is typically called labelled as "reset" in this
> case, functions as both hardware reset and hardware standby mode control.
> It should be asserted (i.e. be set to low level) whenever the sensor is
> expected to be powered off. Typically deasserting it is the last step in
> the sensor's power-up sequence. This applies to nearly all CSI-2 and DVP
> (parallel) camera sensors. (There are some exceptions that use explicitly
> two GPIOs for similar functions but there are very few of them.)

This patch has the reset asserted by the time it gets to
imx355_power_on():

- when coming from runtime PM, the suspend callback asserted it
- when coming from probe, GPIOD_OUT_HIGH asserted it (considering that
  active-low also affects the initial output setting)

Should it be asserted again inside the function, or
should the initial `gpiod_set_value_cansleep()` be removed?