linux-kernel - Re: [PATCH v5 06/10] media: i2c: ov9282: add led

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Message-ID: <v2p627nliqi55pk3w6pjckj5ddozkbgfcam2qbvdjo2w5b6rqx@si5pxcdmt2yr>
Date: Mon, 4 Aug 2025 15:33:34 +0200
From: Richard Leitner <richard.leitner@...ux.dev>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [PATCH v5 06/10] media: i2c: ov9282: add led_mode v4l2 control

On Wed, Jul 30, 2025 at 08:39:46PM +0000, Sakari Ailus wrote:
> Hi Richard,
> 
> On Fri, Jul 11, 2025 at 09:41:52AM +0200, Richard Leitner wrote:
> > Hi Sakari,
> > 
> > On Thu, Jul 10, 2025 at 08:14:07AM +0000, Sakari Ailus wrote:
> > > Hi Richard,
> > > 
> > > On Thu, Jul 10, 2025 at 08:50:24AM +0200, Richard Leitner wrote:
> > > > Hi Sakari,
> > > > 
> > > > thanks for the feedback :)
> > > > 
> > > > On Wed, Jul 09, 2025 at 09:12:57PM +0000, Sakari Ailus wrote:
> > > > > Hi Richard,
> > > > > 
> > > > > Thanks for the update.
> > > > > 
> > > > > On Tue, Jun 17, 2025 at 09:31:40AM +0200, Richard Leitner wrote:
> > > > > > Add V4L2_CID_FLASH_LED_MODE support using the "strobe output enable"
> > > > > > feature of the sensor. This implements following modes:
> > > > > > 
> > > > > >  - V4L2_FLASH_LED_MODE_NONE, which disables the strobe output
> > > > > >  - V4L2_FLASH_LED_MODE_FLASH, which enables the strobe output
> > > > > 
> > > > > I really think you should use a different control for this. The sensor can
> > > > > strobe the flash but it won't control its mode.
> > > > > 
> > > > > How about calling it V4L2_FLASH_STROBE_ENABLE?
> > > > 
> > > > I agree on that. But tbh V4L2_FLASH_STROBE_ENABLE somehow sounds wrong
> > > > to me. As the strobe output in the ov9282 case goes high for the strobe
> > > > duration, what do you think about calling it V4L2_FLASH_STROBE_PULSE?
> > > 
> > > That's how the hardware strobe is supposed to work, there's nothing unusual
> > > in that. How about V4L2_FLASH_HW_STROBE_ENABLE?
> > 
> > Ah. Sorry. I believe I completely misunderstood your previous point.
> > You're not referring to a new menu entry in V4L2_CID_FLASH_LED_MODE,
> > but rather proposing a completely new boolean control, correct?
> 
> Correct.
> 
> > 
> > As this would be separating the V4L2_CID's of "strobe signal source"
> > (aka sensor) and "strobe signal consumer" (aka flash device/LEDs), that
> > makes perfect sense to me now! :)
> > 
> > What are your thoughts on naming it V4L2_FLASH_HW_STROBE_SIGNAL?
> 
> Seems reasonable.

Thanks again for your response. I already sent out a v6 with that
control name. I hope that's fine.

> 
> In order to use the control, the user space would need to know when to use
> it, i.e. when the latching point would be in order to hit a particular
> frame. If the strobe can start before the exposure (and presumably it needs
> to), the latching point is before that point of time. I wonder if pixels
> (as in the pixel array) would be reasonable unit for this as well.
> 
> Does the sensor datasheet shed any light on this? It might be good to add a
> control for that as well.

I'm not sure if pixels is a good unit for that. The strobe duration and
strobe timeout are both defined as µs. Therefore I would prefer to also
use µs for the strobe shift/offset.

The sensor features a control named "strobe shift" which allows to move the
point of time when the strobe starts before/after the start of the exposure.

I've named it V4L2_FLASH_HW_STROBE_SIGNAL_SHIFT in my downstream tree.
What do you think about it?

I have had planned to submit support for the strobe shift/offset control
as soon as this series got accepted. Mainly to keept the series smaller
and easier to handle (at least for me). Tbh I still want to stick to that
approach. Is that fine with you? Or should I include those patches
in this series?

> 
> > 
> > The main reason behind removing the "ENABLE" suffix is that none of
> > the V4L2_CID_FLASH_* controls currently include "ENABLE" in their
> > names. Altough, for example, V4L2_CID_FLASH_CHARGE performs a
> > similar function (en-/disabling the charging of the capacitor).
> > 
> > On the other hand, adding "SIGNAL" to the control name, in my opinion,
> > makes it clearer that it only enables a signal and not some kind of
> > flash device or LED.
> 
> -- 
> Kind regards,
> 
> Sakari Ailus

Thanks again for reviewing the series!

regards;rl