Hi Robert,

On Thu, Mar 26, 2020 at 12:56:37PM +0100, Robert Foss wrote:
...

quoted

quoted

+static int __ov8856_power_on(struct ov8856 *ov8856)
+{
+     struct i2c_client *client = v4l2_get_subdevdata(&ov8856->sd);
+     int ret;
+
+     ret = clk_prepare_enable(ov8856->xvclk);
+     if (ret < 0) {
+             dev_err(&client->dev, "failed to enable xvclk\n");
+             return ret;
+     }
+
+     gpiod_set_value_cansleep(ov8856->reset_gpio, GPIOD_OUT_HIGH);
+
+     ret = regulator_bulk_enable(ARRAY_SIZE(ov8856_supply_names),
+                                 ov8856->supplies);
+     if (ret < 0) {
+             dev_err(&client->dev, "failed to enable regulators\n");
+             goto disable_clk;
+     }
+
+     gpiod_set_value_cansleep(ov8856->reset_gpio, GPIOD_OUT_LOW);
+
+     usleep_range(1500, 1800);

I think you could omit the delay on ACPI based systems. Or just bail out
early in that case.

I'll add a check for reset_gpio being NULL, and skip the sleep for that case.

There could also be a regulator but no GPIO.

I think if you don't have either, then certainly there's no need for a
delay.

...

quoted

quoted

+             ov8856->xvclk = NULL;
+     } else if (IS_ERR(ov8856->xvclk)) {
+             dev_err(&client->dev, "could not get xvclk clock (%ld)\n",
+                     PTR_ERR(ov8856->xvclk));
+             return PTR_ERR(ov8856->xvclk);
+     }
+
+     ret = clk_set_rate(ov8856->xvclk, OV8856_XVCLK_24);

This should either come from platform data, or perhaps it'd be even better
to get the clock rate and use assigned-clock-rates. I guess that's
preferred nowadays.

I'm a bit unsure about what this would look like.

Are you thinking something like the way ext_clk is used in smiapp_core.c?
I went ahead and implemented support for retrieving and storing
'clock-rates' during the ov8856_check_hwcfg() call, and then setting
the rate to the configured rate during probing.

With assigned-clock-rates, you can simply use clk_get_rate().

As you get the actual rate, it could be somewhat off of the intended one.

-- 
Kind regards,

Sakari Ailus

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