Re: [PATCH/RFC v3 5/5] media: Add registration helpers for V4L2 flash sub-devices

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Hi Sakari,

On 04/23/2014 05:24 PM, Sakari Ailus wrote:
Hi Jacek,

On Thu, Apr 17, 2014 at 10:26:44AM +0200, Jacek Anaszewski wrote:
Hi Sakari,

Thanks for the review.

On 04/16/2014 08:21 PM, Sakari Ailus wrote:
Hi Jacek,

Thanks for the update!

[...]
+static inline enum led_brightness v4l2_flash_intensity_to_led_brightness(
+					struct led_ctrl *config,
+					u32 intensity)

Fits on a single line.

+{
+	return intensity / config->step;

Shouldn't you first decrement the minimum before the division?

Brightness level 0 means that led is off. Let's consider following case:

intensity - 15625
config->step - 15625
intensity / config->step = 1 (the lowest possible current level)

In V4L2 controls the minimum is not off, and zero might not be a possible
value since minimum isn't divisible by step.

I wonder how to best take that into account.

I've assumed that in MODE_TORCH a led is always on. Switching
the mode to MODE_FLASH or MODE_OFF turns the led off.
This way we avoid the problem with converting 0 uA value to
led_brightness, as available torch brightness levels start from
the minimum current level value and turning the led off is
accomplished on transition to MODE_OFF or MODE_FLASH, by
calling brightness_set op with led_brightness = 0.

[...]

+/*
+ * V4L2 subdev internal operations
+ */
+
+static int v4l2_flash_open(struct v4l2_subdev *sd, struct v4l2_subdev_fh *fh)
+{
+	struct v4l2_flash *v4l2_flash = v4l2_subdev_to_v4l2_flash(sd);
+	struct led_classdev *led_cdev = v4l2_flash->led_cdev;
+
+	mutex_lock(&led_cdev->led_lock);
+	v4l2_call_flash_op(sysfs_lock, led_cdev);

Have you thought about device power management yet?

Having in mind that the V4L2 Flash sub-device is only a wrapper
for LED driver, shouldn't power management be left to the
drivers?

How does the LED controller driver know it needs to power the device up in
that case?

I think an s_power() op which uses PM runtime to set the power state until
V4L2 sub-device switches to it should be enough. But I'm fine leaving it out
from this patchset.


This solution looks reasonable.

Regards,
Jacek Anaszewski


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